Doctor of Philosophy / Department of Animal Sciences and Industry / Evan C. Titgemeyer / Two experiments were conducted to evaluate the effects of late gestation and early lactation on the nutritional status of beef heifers fed low-quality, warm-season grass hay. The first experiment compared DMI, DM digestibility, and ruminal dynamics of pregnant and lactating beef heifers to non-gestating, non-lactating heifers of a similar age and size. This study demonstrated that pregnant heifers ate less than non-pregnant heifers while maintaining similar digestibilities. Intake was similar between lactating and non-lactating, though DM digestibility increased postpartum in lactating heifers. Ruminoreticular fill was less for pregnant than for non-pregnant heifers; ruminoreticular fill was similar regardless of lactation status. Ruminal NH3 increased with increasing intakes throughout the study. Lactating heifers had less ruminal NH3 than non-lactating heifers. Total ruminal VFA concentration was similar from 10 wk prepartum through 10 wk postpartum except at 2 wk prepartum when gestating heifers had less total ruminal VFA concentration. The second experiment compared DMI, DM digestibility, passage rate, and plasma glucose and BHBA concentrations between pregnant heifers, pregnant cows, lactating heifers, and lactating cows which were fed low-quality, warm-season grass hay supplemented with 450 g/d of soybean meal. This study demonstrated that DMI increased with progressing gestation in heifers. Lactating heifers had greater intake than other groups postpartum. DM digestibility decreased with advancing gestation; gestating animals had greater digestibility than non-gestating animals. Lactation status did not influence DM digestibility, though lactating heifers had greater digestibility from 3 to 7 wk postpartum. Digestibility was not influenced by age. Pregnant animals had faster digesta passage rates than non-pregnant counterparts. Plasma glucose concentration increased during the prepartum period; pregnant and lactating animals had lesser plasma glucose concentrations than non-gestating, non-lactating animals. Plasma BHBA concentration was greater in pregnant and lactating animals than in non-pregnant and non-lactating animal; age was not an influence on BHBA concentration. Calves from mature cows grew faster than calves from heifers. These studies showed that beef heifers do not have the same patterns of intake as mature cows during late gestation. Heifers and their calves exhibited poorer performance when compared to mature cows when fed low-quality, warm-season grass hay.

Submitted by Marcos Anselmo (marcos.anselmo@unipampa.edu.br) on 2018-09-28T18:53:23Z No. of bitstreams: 1 JANICE MACHADO DE MACHADO VILLELA.pdf: 769666 bytes, checksum: 37e9705b299aec59293356729fda9547 (MD5) / Approved for entry into archive by Marcos Anselmo (marcos.anselmo@unipampa.edu.br) on 2018-09-28T18:53:35Z (GMT) No. of bitstreams: 1 JANICE MACHADO DE MACHADO VILLELA.pdf: 769666 bytes, checksum: 37e9705b299aec59293356729fda9547 (MD5) / Made available in DSpace on 2018-09-28T18:53:35Z (GMT). No. of bitstreams: 1 JANICE MACHADO DE MACHADO VILLELA.pdf: 769666 bytes, checksum: 37e9705b299aec59293356729fda9547 (MD5) Previous issue date: 2018 / O parto é uma importante fase do sistema produtivo leiteiro, e impõe grande desafio para a vaca. Além do risco de doenças clínicas e subclínicas, favorecidas pela imunossupressão e alterações hormonais, as vacas podem sofrer distocias, que são partos marcados por dificuldade, tempo prolongado e necessidade de assistência para remoção do feto. Por ser multifatorial, além das causas maternas e fetais relacionadas à distocia, pode haver interação com variáveis comportamentais, ambientais e de manejo. O impacto da distocia no sistema produtivo está relacionado à ocorrência de doenças, o que aumenta o risco de descarte e morte, tanto para as vacas quanto para suas crias, impactando nos custos de produção e afetando a composição e longevidade do rebanho. Portanto, a presente dissertação teve como objetivos: identificar os fatores de risco associados à distocia e seu impacto sobre as doenças do período de transição pós-parto e sobre a produção de leite em vacas leiteiras; e avaliar se bezerras leiteiras nascidas de partos distócicos tiveram seu desenvolvimento, saúde, reprodução e produção de leite prejudicados. Para responder aos objetivos, realizou-se um estudo observacional retrospectivo utilizando registros de uma propriedade leiteira no Rio Grande do Sul, obtidos do software de gerenciamento leiteiro Dairy Plan C-21(GEA). O estudo foi dividido em dois experimentos, cujos resultados estão em um artigo científico. Para responder a um dos objetivos do primeiro experimento, foram analisados dados de 1.001 partos de vacas Holandesas, primíparas e multíparas, ocorridos entre 2013 e 2017, agrupadas em partos eutócicos e distócicos. As variáveis incluídas como preditoras de risco de distocia foram idade da vaca, categoria da vaca (primípara vs multípara), distocia ao nascimento, sexo do bezerro, tipo de parto, viabilidade do bezerro, estação climática no parto e ano. Para determinar o impacto da distocia sobre as doenças do pós-parto e produção de leite, foram analisados separadamente os dados das vacas primíparas (n= 540) e multíparas (n=461). Foram avaliadas as taxas de doenças clínicas como mastite, metrite, retenção de placenta e outras, bem como o número de episódios ocorridos, além das taxas de descarte e morte. A incidência de partos distócicos foi de 10,4% e os fatores de risco significativos para ocorrência de distocias foi o nascimento de bezerros machos, gêmeos, natimortos e partos ocorridos no inverno. Observou-se uma alta taxa de doenças clínicas no pós-parto e um risco aumentado para desenvolvimento de metrite em vacas multíparas distócicas. Para responder ao objetivo do segundo experimento, foram analisados registros de 447 bezerras nascidas na propriedade entre 2012 e 2015 agrupadas como nascidas de partos eutócicos ou distócicos. O impacto da distocia sobre a saúde, desenvolvimento e produção das bezerras foi analisado mediante avaliação dos dados de peso ao nascimento, 30 e 60 dias de idade, ocorrência de doenças até os 60 dias e até os 365 dias de idade, bem como o número de eventos ocorridos nestes períodos e as taxas de mortalidade e descarte. Também se avaliou o número de inseminações por concepção, a idade ao primeiro parto, taxas de distocia e natimortos, as doenças clínicas mastite, metrite, retenção de placenta e outras ocorridas após o primeiro parto e a produção de leite na primeira lactação. Observou-se que bezerras crias de partos distócicos apresentaram maiores taxas de metrite após o primeiro parto. Outros parâmetros não foram afetados pela distocia. / Parturition is an important process of the dairy production system and imposes a great challenge to the cow. In addition to the risk of clinical and subclinical diseases favored by immunosuppression and hormonal changes, cows may suffer from dystocia, which are difficulty deliveries with prolonged time and sometimes the need for assist in fetal removal. Since it is multifactorial, in addition to the maternal and fetal causes related to dystocia, it could have interaction with behavioral, environmental and management variables. The impact of dystocia on the productive system is related to the occurrence of diseases, which increases the risk of discarding the cows from the dairy and even death of the cows and their offspring, impacting production costs and affecting the composition and longevity of the herd. Therefore, the present dissertation had as objectives: identify the risk factors associated with dystocia and its impact on the diseases of the postpartum transition period and on milk production in dairy cows; and evaluate if dairy heifers born from a dystocic birth had their development, health, reproduction or milk production impaired. In order to respond to the objectives, a retrospective observational study was carried out using records from a dairy farm in Rio Grande do Sul, using Dairy Plan C-21 dairy management software (GEA). The study was divided into two experiments, which the results were published in a scientific paper. In order to achieve one of the objectives of the first experiment, data collected between 2013 and 2017, from 1,001 primiparous Holstein’s heifers and multiparous Holstein’s cows, grouped into normal or difficult birth was analyzed. The variables included as predictors of risk of dystocia were age, category (primiparous vs. multiparous), dystocic birth, calf sex, type of delivery, calf viability, climatic season at calving and year. To determine the impact of dystocia on postpartum diseases and milk production, data from primiparous cows (n = 540) and multiparous cows (n = 461) were analyzed separately. Rates of clinical diseases such as mastitis, metritis, retained placenta and others, as well as the number of episodes occurred and rates of discard or death were evaluated. The incidence of dystocia was 10.4% and the significant risk factors to the occurrence of dystocia were the birth of male calves, twins, stillbirths and births during winter time. There was a high rate of postpartum clinical disease and an increased risk of developing metritis in distocic multiparous cows. In order to achieve the second experiment, we analyzed the records from 447 calves born at the farm between 2012 and 2015 and grouped as born from normal or difficult births. The impact of dystocia on the health, development and production of heifers was analyzed by weight at birth, 30 and 60 days of age, occurrence of diseases up to 60 days and up to 365 days of age, as well as the number of events occurred in these periods and mortality and discharge rates. The number of inseminations per conception, age at first calving, dystocia and stillbirth rates, clinical mastitis, metritis, retained placenta and others after first calving and milk production at the first lactation were also evaluated. It was observed that heifers born from a dystocic parturition had higher rates of metritis on their first calving. Other parameters were not affected by dystocia.

O presente estudo visou caracterizar a secreção de PRL e estudar suas interrelações com a PGFM durante a pré-luteólise, luteólise e pós-luteólise em éguas (Experimento 1); avaliar o efeito da inibição de PRL e PGF2α na luteólise e definir a sincronia entre PRL e PGFM em novilhas (Experimento 2); definir a sincronia entre PRL e PGFM em éguas (Experimento 3); e avaliar a constante estimulação da PRL durante o ciclo estral em éguas (Experimento 4). No experimento 1 em éguas, amostras de sangue foram coletadas durante as 24 h da préluteólise, luteólise e pós-luteólise. As concentrações de PRL e PGFM foram rítmicas, sendo a duração dos pulsos de PRL de 5 h, com intervalos de 7,5 h entre pulsos e 12 h entre picos. Durante a luteólise e pós-luteólise, os pulsos de PRL foram mais proeminentes, as concentrações de PRL durante um pulso de PGFM foram maiores no pico de PGFM e notouse uma maior sincronia entre picos de PRL e PGFM. No experimento 2 em novilhas, as secreções de PRL e PGF2α foram inibidas durante a luteólise. A inibição da PRL associou-se a maiores concentrações de P4 e LH, sem efeito sobre a PGFM. Entretanto, a inibição da PGF2α associou-se a uma queda nas concentrações de PRL. A mensuração da área do CL mostrou-se eficiente em detectar a luteólise. No experimento 3 em éguas, no verão e outono, inibiu-se a secreção de PGF2α e PRL no Dia 14. As concentrações de PGFM foram reduzidas com a inibição de PGF2α, mas não com a inibição da PRL. No verão, a inibição tanto de PRL quanto de PGF2α reduziu as concentrações de PRL. As concentrações de PGFM não diferiram entre o verão e o outono, enquanto que as concentrações de PRL foram menores no outono. No experimento 4 em éguas, estimulou-se a secreção de PRL a cada 8 h. Amostras de sangue foram coletadas a cada 12 h do Dia 13 até a ovulação e a cada hora por 12 h no Dia 14. A estimulação repetida da PRL não aparentou manter as concentrações de PRL elevadas após o Dia 14. Nas amostras a cada hora, concentrações de PRL atingiram um valor máximo 4 horas após a estimulação e os pulsos de PRL foram aumentados. O aumento na PRL não afetou a PGFM, P4 e fluxo sanguíneo do CL. Entretanto, a estimulação da PRL quebrou a sincronia entre PGFM e PRL. Estão contidos nessa dissertação o primeiro relato em éguas sobre a caracterização e ritmicidade de pulsos de PRL, sincronia entre pulsos de PRL e PGFM e maior atividade da PRL durante a luteólise e pós-luteólise. A inibição da PRL interferiu na secreção de P4 em novilhas, mas foi confundida pelo aumento de LH. A sincronia entre pulsos de PGFM e PRL representa um efeito positivo da PGF2α sobre a PRL, tanto em éguas quanto em novilhas. / The aim of the present study was to characterize the PRL secretion and study the relationship between PRL and PGFM during preluteolysis, luteolysis and postluteolysis in mares (Experiment 1); evaluate the effect of PRL and PGF2α inhibition on luteolysis and define the synchrony between PRL and PGFM in heifers (Experiment 2); define the synchrony between PRL and PGFM in mares (Experiment 3); and evaluate the frequent stimulation of PRL during the estrous cycle in mares (Experiment 4). On experiment 1 in mares, blood samples were collected during the 24 h of preluteolysis, luteolysis and postluteolysis. Concentrations of PRL and PGFM were rhythmic. Prolactin pulses had 5h of duration, interval of 7,5 h between pulses, and 12 h between peaks. Pulses of PRL were more prominent during luteolysis and postluteolysis. Concentrations of PRL during PGFM pulses differ during luteolysis and postluteolysis, and were greater at the peak of PGFM. The synchrony between peaks of PRL and PGFM was greater during luteolysis and postluteolysis. On experiment 2 in heifers, the secretion of PRL and PGF2α were inhibited during luteolysis. The PRL inhibition was associated with greater concentrations of P4 and LH. The inhibition of PGF2α was associated with a decrease on PRL concentrations, but no effect on PGFM was observed after PRL inhibition. The CL area measurement was an efficient method to target luteolysis. On experiment 3 in mares, in summer and autumn, secretion of PGF2α and PRL were inhibited on Day 14. The inhibition of PGF2α reduced PGFM concentrations. No effect on PGFM was observed after PRL inhibition. Concentrations of PGFM were not different between summer and autumn, and PRL concentrations were low in the autumn. In the summer, PRL inhibition reduced PGF2α concentrations. On experiment 4 in mares, PRL was stimulated every 8 h. Blood samples were collected every 12 h from Day 13 to ovulation, and every hour for 12 h on Day 14. The frequent stimulation on PRL did not appear to maintain higher concentrations of PRL after Day 14. On hourly samples, concentrations of PRL reached maximum value 4 h after stimulation and pulses of PRL were increased. The increase on PRL did not affect PGFM, P4, and blood flow of the CL. The synchrony between PGFM and PRL was partially disrupted by PRL stimulation. This was the first report on characterization and rhythm of PRL pulses, synchrony between PRL and PGFM pulses, and greater PRL activity during luteolysis and postluteolysis. The inhibition of PRL interfered with P4 secretion in heifers, but was confounded by the LH increase. In mares and heifers, the synchrony between PGFM and PRL pulses represents a positive effect of PGF2α on PRL.

With feed costs representing on average 65% of the total cost of production improvements in feed efficiency could have a major impact on the beef industry. Postweaning performance and feed efficiency data were collected on 114 heifers born on the University of Arizona's V bar V Ranch. Residual feed intake (RFI) was significantly correlated with dry matter intake (DMI) (r = 0.46) and G:F (r = -0.43), while G:F was moderately correlated with initial age (r = -0.54), initial body weight (r = -0.40), and average daily gain (ADG) (r = 0.68). Residual gain (RG) was moderately correlated with RFI (r = -0.41) and highly correlated with ADG (0.62) and G:F (0.73). In addition, RG was significantly correlated (r = -0.21) with initial weight suggesting that selection for RG could lead to increased cow mature size. Heifers were sorted into three breed categories: Hereford, Hereford cross, and Wagyu cross and breed effect on performance and feed efficiency traits were analyzed. Significant differences in DMI, FCR, and RG were noted, but likely due to significant differences in age at the time of testing. RFI was not significantly different between breed groups, suggesting that RFI is less influenced by animal age than other measures of feed efficiency. In addition, sires of study heifers with 5 or more progeny were selected and progeny performance and feed efficiency traits were compared between sires. No significant differences in ADG, RFI, FCR, or RG were noted between sire progeny. This was likely due to an insufficient number of progeny used in the trial. Further research and an increased number of animals used may uncover significant impacts of sire on RFI.

The objective of this dissertation was to determine the feeding motivation of dairy heifers and to determine management factors that contribute to satiety in limit-fed dairy heifers. The first study of this dissertation determined the difference in behavioural patterns between limit-fed and ad libitum-fed dairy heifers so that we may understand how limit feeding diverges from normal behaviour. Limit-fed heifers were found to decrease time spent feeding, consume less DM, and increase their feeding rate across the day in comparison to ad libitum-fed heifers. Additionally, the diurnal patterns of ad libitum-fed heifers were much closer to normal behaviour as they consisted of several short, small meals distributed throughout the day. The next three studies examined the management factors of frequency of feed provision and feed bunk space and how these may impact the behaviour of heifers. Increased frequency of feed provision did result in more distribution of feeding activity throughout the day but also imposed feeding amounts that were likely insufficient to achieve satiety. Heifers fed once daily likely experienced satiety in the short term and did spend the most time feeding throughout the day but the diurnal patterns of these heifers did not allow for expression of normal foraging behaviour. Providing increased feed bunk space did not allow limit-fed heifers to spend more time feeding or impact competition within a pen whereas providing straw alongside of a nutrient-dense TMR did result in more normal diurnal patterns, albeit with an increase in competitive behaviour. There was no interaction found between feed bunk space and frequency of feed provision, indicating that limit-fed heifers must be provided with sufficient bunk space to feed simultaneously. Heifers provided with un-restricted bunk space did gain more and were more feed efficient and less variable in feeding time than heifers given restricted bunk space. Feeding once daily resulted in an increase in competition but also enabled heifers to gain well and to spend more time feeding each day. The remaining studies sought to quantify whether a preference for supplementary feed exists in limit-fed heifers and whether heifers will work, and to what extent, for this extra feed. The results indicated that heifers will consume similar amounts of supplementary long or short straw if provided to them alongside of a limit-fed TMR. The limit-fed heifers do, however, show a clear preference for long straw when offered the choice, suggesting that they find long straw to be more satisfactory for achieving rumen fill and/or meeting their behavioural foraging needs. Heifers were also found to work harder (push more weight), spend less time feeding and ruminating, and consume feed faster when provided a high-concentrate, limit-fed ration than when provided a high-forage, ad libitum-fed ration, suggesting that these animals are experiencing feelings of hunger and may not be physically or behaviourally satisfied. These findings indicate that there are clear behavioural differences between limit-fed and ad libitum-fed dairy heifers. Management factors, such as frequency of feed provision and feed bunk space, may be altered in such a way as to provide some benefit to the animals but are limited in their ability to normalize feeding behaviour and diurnal patterns. Provision of supplemental, long particle low-nutritive roughage (i.e. straw) aids much more in allowing limit-fed heifers to achieve satiety and is considered a desirable resource by the animals, as evidenced through their willingness to work for this supplemental feed. / Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA)/University of Guelph Production Systems research grant and a Campbell Centre for the Study of Animal Welfare research grant. This project was also supported through contributions from the Canadian Foundation for Innovation (CFI) and the Ontario Research Fund. Angela Greter was supported through NSERC Alexander Graham Bell Canadian Graduate Student scholarship

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 347-358). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 347-358). Also available on the Internet.

Master of Science / Department of Animal Sciences and Industry / Karol E. Fike / Trace mineral supplementation is necessary for proper reproductive success. Little research has evaluated the effect of an injectable trace mineral product, in conjunction with a dietary mineral supplementation program, on reproduction. This thesis includes two separate studies evaluating the use of an injectable trace mineral product, in addition to a dietary mineral program, on the reproductive success of yearling bulls and heifers. In the first study, we hypothesized that when dietary trace mineral needs are met, administration of an injectable trace mineral product to developing beef bulls would cause a short-term increase in circulating trace mineral concentrations, but not alter semen quality nor ability to pass a breeding soundness examination. Trace mineral treatment did not affect scrotal circumferences and BW of bulls throughout the trial (P [equal to or greater than] 0.20). Trace Mineral bulls had greater (P [equal to or less than] 0.0001) trace mineral concentrations at 8 h post-treatment than Control bulls. Semen trace mineral concentrations on d 42 and 91 were similar (P [equal to or greater than] 0.52) between treatments. Sperm parameters improved (P [equal to or less than] 0.003) from d 42 to 91, but did not differ (P [equal to or greater than] 0.06) between treatments. A similar (P = 0.94) percentage of Trace Mineral (67%) and Control (68%) bulls passed a BSE 91 d post-treatment. In the present study, supplemental trace mineral injection was successful at raising circulating trace mineral levels, but did not alter semen trace mineral levels nor improve semen quality. In the second study we hypothesized that when dietary trace mineral needs are met, the use of an injectable trace mineral product in developing heifers would not affect pregnancy rates at single service fixed-time artificial insemination (FTAI). Trace Mineral heifers had greater (P = 0.02) pregnancy rates (51.28%) than Control heifers (25.58%). The percentage of Trace Mineral (30.77%) and Control heifers (47.50%) that displayed estrous behavior prior to FTAI as indicated by a red estrous detection patch was not different (P = 0.13) between treatments. In the present study, despite dietary trace mineral requirements being met, use of an injectable trace mineral injection improved pregnancy rates following FTAI, but did not affect estrous behavior.

O presente estudo visou caracterizar a secreção de PRL e estudar suas interrelações com a PGFM durante a pré-luteólise, luteólise e pós-luteólise em éguas (Experimento 1); avaliar o efeito da inibição de PRL e PGF2α na luteólise e definir a sincronia entre PRL e PGFM em novilhas (Experimento 2); definir a sincronia entre PRL e PGFM em éguas (Experimento 3); e avaliar a constante estimulação da PRL durante o ciclo estral em éguas (Experimento 4). No experimento 1 em éguas, amostras de sangue foram coletadas durante as 24 h da préluteólise, luteólise e pós-luteólise. As concentrações de PRL e PGFM foram rítmicas, sendo a duração dos pulsos de PRL de 5 h, com intervalos de 7,5 h entre pulsos e 12 h entre picos. Durante a luteólise e pós-luteólise, os pulsos de PRL foram mais proeminentes, as concentrações de PRL durante um pulso de PGFM foram maiores no pico de PGFM e notouse uma maior sincronia entre picos de PRL e PGFM. No experimento 2 em novilhas, as secreções de PRL e PGF2α foram inibidas durante a luteólise. A inibição da PRL associou-se a maiores concentrações de P4 e LH, sem efeito sobre a PGFM. Entretanto, a inibição da PGF2α associou-se a uma queda nas concentrações de PRL. A mensuração da área do CL mostrou-se eficiente em detectar a luteólise. No experimento 3 em éguas, no verão e outono, inibiu-se a secreção de PGF2α e PRL no Dia 14. As concentrações de PGFM foram reduzidas com a inibição de PGF2α, mas não com a inibição da PRL. No verão, a inibição tanto de PRL quanto de PGF2α reduziu as concentrações de PRL. As concentrações de PGFM não diferiram entre o verão e o outono, enquanto que as concentrações de PRL foram menores no outono. No experimento 4 em éguas, estimulou-se a secreção de PRL a cada 8 h. Amostras de sangue foram coletadas a cada 12 h do Dia 13 até a ovulação e a cada hora por 12 h no Dia 14. A estimulação repetida da PRL não aparentou manter as concentrações de PRL elevadas após o Dia 14. Nas amostras a cada hora, concentrações de PRL atingiram um valor máximo 4 horas após a estimulação e os pulsos de PRL foram aumentados. O aumento na PRL não afetou a PGFM, P4 e fluxo sanguíneo do CL. Entretanto, a estimulação da PRL quebrou a sincronia entre PGFM e PRL. Estão contidos nessa dissertação o primeiro relato em éguas sobre a caracterização e ritmicidade de pulsos de PRL, sincronia entre pulsos de PRL e PGFM e maior atividade da PRL durante a luteólise e pós-luteólise. A inibição da PRL interferiu na secreção de P4 em novilhas, mas foi confundida pelo aumento de LH. A sincronia entre pulsos de PGFM e PRL representa um efeito positivo da PGF2α sobre a PRL, tanto em éguas quanto em novilhas. / The aim of the present study was to characterize the PRL secretion and study the relationship between PRL and PGFM during preluteolysis, luteolysis and postluteolysis in mares (Experiment 1); evaluate the effect of PRL and PGF2α inhibition on luteolysis and define the synchrony between PRL and PGFM in heifers (Experiment 2); define the synchrony between PRL and PGFM in mares (Experiment 3); and evaluate the frequent stimulation of PRL during the estrous cycle in mares (Experiment 4). On experiment 1 in mares, blood samples were collected during the 24 h of preluteolysis, luteolysis and postluteolysis. Concentrations of PRL and PGFM were rhythmic. Prolactin pulses had 5h of duration, interval of 7,5 h between pulses, and 12 h between peaks. Pulses of PRL were more prominent during luteolysis and postluteolysis. Concentrations of PRL during PGFM pulses differ during luteolysis and postluteolysis, and were greater at the peak of PGFM. The synchrony between peaks of PRL and PGFM was greater during luteolysis and postluteolysis. On experiment 2 in heifers, the secretion of PRL and PGF2α were inhibited during luteolysis. The PRL inhibition was associated with greater concentrations of P4 and LH. The inhibition of PGF2α was associated with a decrease on PRL concentrations, but no effect on PGFM was observed after PRL inhibition. The CL area measurement was an efficient method to target luteolysis. On experiment 3 in mares, in summer and autumn, secretion of PGF2α and PRL were inhibited on Day 14. The inhibition of PGF2α reduced PGFM concentrations. No effect on PGFM was observed after PRL inhibition. Concentrations of PGFM were not different between summer and autumn, and PRL concentrations were low in the autumn. In the summer, PRL inhibition reduced PGF2α concentrations. On experiment 4 in mares, PRL was stimulated every 8 h. Blood samples were collected every 12 h from Day 13 to ovulation, and every hour for 12 h on Day 14. The frequent stimulation on PRL did not appear to maintain higher concentrations of PRL after Day 14. On hourly samples, concentrations of PRL reached maximum value 4 h after stimulation and pulses of PRL were increased. The increase on PRL did not affect PGFM, P4, and blood flow of the CL. The synchrony between PGFM and PRL was partially disrupted by PRL stimulation. This was the first report on characterization and rhythm of PRL pulses, synchrony between PRL and PGFM pulses, and greater PRL activity during luteolysis and postluteolysis. The inhibition of PRL interfered with P4 secretion in heifers, but was confounded by the LH increase. In mares and heifers, the synchrony between PGFM and PRL pulses represents a positive effect of PGF2α on PRL.

<p>The objective of this study was to evaluate the long-term effects that early life events have on heifer growth up to 400 d of age, heifer conception rate, survivability through first lactation, and first lactation milk production of calves raised in automatic calf feeders. Chapter one evaluates possible early life variables that would affect heifer growth and lifetime production as well as research that has been done to predict future growth. The major points discussed include pre-weaning feeding strategies, automatic calf feeding systems, respiratory disease and ways to diagnose cattle with this disease, and the impact of early life growth on the future productivity of the dairy cow.<br></p> <p>The second chapter discusses in detail the process of creating a predictive equation using significant early life variables that affect Holstein heifer growth up to 400 d of age. Variables collected for the growth analysis included sixty d cumulative milk consumption (MC), serum total protein values, respiratory disease and scours incidences, genetic body size, birthweights, and incremental body weight variables on a commercial dairy farm from October 1, 2015 to January 1, 2019. Calves were fed pasteurized whole milk through an automated calf feeding system (feeders = 8) for 60 d (range: 48 – 126d), with a 30% Crude Protein (CP) and 5% Crude Fat enhancer added at 20 g/L of milk. Calves were weighed at birth and several other times prior to calving. Average birth weight of calves was 40.6 ± 4.9 kg (mean ± SD), serum total protein was 6.7 ± 0.63 g/dL, and cumulative 60 d MC was 508.1 ± 67.3 L with a range of 179.9 to 785.1 L. Daily body weights were predicted for individual animals using a third order orthogonal polynomial to model growth curves. The linear and quadratic effects of cumulative 60 d milk consumption, birthweight, feeder, yr born, season born, respiratory incidence, and genetic body size score were significant (<i>P</i><0.0001) when predicting heifer body weight at 400 d (pBW₄₀₀) of age (R²=0.31). There was up to a 263 kg difference in pBW₄₀₀between the heaviest and lightest animal. Birthweight had a significant effect on predicted weights up to 400 d (<i>P</i><0.0001), and for every 1 kg increase in birthweight, there was a 2.5 kg increase in pBW₄₀₀. The quadratic effect of cumulative 60 d MC was significant for pBW₄₀₀ (<i>P</i><0.0001). When 60 d MC was divided into quartiles, heifers had the highest pBW₄₀₀in the third quartile, when 60 d MC was between 507.8 and 552.5 L. Body size composite (genomic index) showed a 21.5 kg difference in pBW₄₀₀ between the top and bottom 25^th percentile of heifers. Heifers were 4.2 kg lighter at 400 d if treated for respiratory disease 3+ times during the first 60 d of life, compared to heifers not treated for respiratory disease.</p> <p>The third chapter utilizes the data described in chapter two and followed those heifers through breeding and first lactation. Heifer conception age and 280 d first lactation milk production (280M) were collected. Average age at conception was 437.5 ± 45.0 d; range of 308 to 631 d (n=5,193), and average 280M was 9,305 ± 1,371.8 kg; range of 712-13,358 kg (n=1,324). Heifer conception age was impacted by season, yr, and the quadratic effects of predicted bodyweight at 300 d of age (pBW₃₀₀) and ADG (0-400; all <i>P</i> < 0.05; total model R² = 0.08). Season born, ADG (0 - 400 d), genomic milk, and the linear effect of heifer conception age had a significant impact on 280M (all <i>P</i> < 0.05; R² = 0.28). For every 1 kg increase in genomic milk value there is 1.42 kg increase in first lactation 280M. Calves not diagnosed with bovine respiratory disease (BRD) from 60-120 d old had a significantly higher chance for survival to first lactation than animals treated three or more times for BRD (hazard ratio = 0.71, 95% CI = 0.574 to 0.886, <i>P </i>= 0.0023, Table 3.3). Heifers treated twice or more for BRD had reduced likelihood to become pregnant than heifers not treated for BRD from 60-120 d (twice <i>P </i>= 0.02; three or more <i>P </i>= 0.05). </p> <p>In conclusion, the results from this thesis support that early life events in Holstein heifers continue to influence future growth and productivity. Future research aims to validate the predictive equation generated in chapter two on farm as well as adapt the equation to other farms allowing them to utilize it as well. The goal is to have farms utilize this tool to aid in their replacement heifer management decisions and to select the most productive heifers for the future of their herds. </p>