No description available.

The objective of the present study was to evaluate the effects of low input development protocols on Southeastern replacement beef females and their offspring. Fall and spring calving crossbred beef heifers managed through one of two heifer development programs (low input, LOW or conventionally developed, CON) were evaluated for metrics of uterine artery hemodynamics, patterns of heifer and offspring growth, postpartum reproductive performance, and economic efficiency. There were significant treatment × season (P = 0.0001) and season × day (P = 0.003) interactions on heifer body weight (BW) during gestation. There was a season × day interaction on total blood flow (TBF; P = 0.05) whereby TBF increased as gestation progressed and spring calving heifers displayed increased TBF. When adjusted for BW, an additional main effect of treatment was observed (P = 0.0007) in which LOW heifers had increased TBF compared to CON heifers. There were no significant main effects of treatment or season or interactions thereof on the proportion of females cycling at the start of the breeding season (P > 0.05). Additionally, there were main effects of treatment (P = 0.0095; P = 0.02) and season (P = 0.012; P = 0.007) on calf ADG and weaning weights, respectively whereby calves born to CON females grew faster than calves born to LOW heifers, and SPRING calves gained more rapidly than FALL calves. Partial budgeting demonstrated that LOW bred heifers were $250/hd less expensive to purchase than CON heifers due to lighter BW. Calves born to LOW females yielded $6.38 less per calf compared to CON calves. The discrepancy in reproductive efficiency coupled with the failure of LOW females to achieve BW similar to CON females resulted in a difference of $403/hd in average cull value between LOW and CON females in which CON females were worth more. Thus, CON females were $159.18 more profitable than LOW females when purchased as bred heifers and sold at the weaning of their first calf. In conclusion, though uterine artery BF was not negatively affected, low input heifer development resulted in sub-optimal heifer growth, poor first calf performance, and inadequate reproductive efficiency.

No description available.

No description available.

The overall objective of this project was to investigate the role of locally derived growth factors and extracellular matrix proteins in regulating prepubertal heifer mammary development. In the first experiment, short-term treatment of heifers with GH or E increased proliferation of mammary epithelial cells. Coinciding with increased epithelial cell proliferation, IGF-I protein increased and IGFBP-3 protein decreased within mammary tissues. Thus, proliferation was associated with an apparent net increase in the biological availability of IGF-I within the mammary gland. In the second experiment, decreased mammary development and epithelial cell proliferation in response to ovariectomy coincided with decreased mammary expression of IGF-I mRNA and decreased binding of IGF-I to mammary microsomes. Taken together, these results imply an important role for locally derived IGF-I in regulating heifer mammary development. However, in contrast to our hypothesis, IGF-I mRNA did not differ between cleared or intact mammary fat pad, suggesting that expression of IGF-I mRNA is not regulated by epithelial:stromal interactions. Neither ovariectomy or epithelial:stromal interactions influenced the mRNA expression of IGFBP-3 or IGFBP-5 within mammary tissues. Ovariectomy increased the proportion of ERa positive mammary epithelial cells. In contrast, GH administration to prepubertal heifers did not influence the proportion of ERa-positive epithelial cells. Interestingly, mammary development was more severely affected in heifers ovariectomized before six weeks of age than heifers ovariectomized at three months of age, implying a critical period of ovarian stimulation during the first six weeks of age. Localization of laminin, fibronectin, and collagen in mammary parenchyma suggested specific roles for extracellular matrix proteins in regulating mammary development and ductal morphogenesis. Laminin was decreased and fibronectin was increased by ovariectomy, suggesting a possible role for interactions between the ovary and extracellular matrix proteins within the heifer mammary gland. Finally, the mitogenic capacities of mammary tissue extracts from control and ovariectomized heifers did not differ in their ability to stimulate in vitro proliferation of MAC-T cells. In conclusion, the overall results support the hypothesis that locally derived IGF-I regulates prepubertal heifer mammary development. However, ERa expression and extracellular matrix proteins also appear to be important regulators of heifer mammary development. / Ph. D.

The objectives of this study were to determine the effects of handling peri-puberal heifers for 2 h each week on in-chute behavior, isolation behavior, and the time required for each heifer to leave the testing area; and to determine if the location of the facial hair whorl was associated with any of the behavior scores or social dominance order. Crossbred beef heifers (n = 146) were assigned to be walked through, sorted and moved through a chute for 2 hr each wk for 20 wk (HANDLED) or allowed to remain on pasture unless handling was required to treat an injury or disease (CONTROL). In-chute behavior, isolation behavior and exit times were observed and scored at the beginning (0 wk), middle (10 wk) and end of the experiment (20 wk). The facial hair whorl on each heifer was classified as being high (above the eyes), middle (between the eyes), or low (below the eyes). At the end of the experiment pairs of heifers in the HANDLED group competed for a feed source and a social dominance order was estimated. Weekly handling decreased in-chute behavior scores of heifers with facial hair whorl positions classified as medium or low, but not in heifers that exhibited a hair whorl high on their face. Cattle in the HANDLED treatment group which had an initial isolation score of 2 or 3 had the greatest improvement in temperament over the entire experiment when compared to CONTROL animals with the same initial isolation score. The calmest heifers were not negatively affected by the handling, while the most agitated animals in the HANDLED had a similar overall change in isolation score as those animals in the CONTROL group. This indicates that while weekly handling improved the temperament and behavior of heifers with intermediate temperament rating at the outset of the experiment, weekly handling seemed unnecessary for the calmest heifers and did not have a beneficial effect on the heifers rated as the most nervous and agitated at the beginning of the experiment. Social dominance rankings were positively correlated (P < 0.10) with final in-chute behavior scores, but not with the other behavior scores or heifer body weight. Cattle with the hair whorls in the middle of the forehead had higher mean social dominant rank than those with hair whorls higher or lower on the face (P < 0.03). Overall, the results of this experiment indicate that behavior testing can reveal differences in the temperament of heifers and that, other than the most nervous and agitated heifers; repeated handling could serve to improve the temperament of the animals. / Master of Science

ABSTRACT: Study One - Our objective was to characterize mature range cows based on intake and grazing activity. Starting in the early spring of 2013, 4 experiments were conducted. First, mature range cows (n = 137) were fitted with radio frequency identification tags (RFID) and placed in a dry-lot pen equipped with GrowSafe® technology to monitor DMI of alfalfa hay. These data were then used to assign cows a residual feed intake (RFI) value utilizing the National Research Council (NRC) (1996) model to predict intake of beef cattle. Cattle with negative and positive RFI were characterized as low-intake and high-intake, respectively. In addition, the following data were also recorded: weight (kg), age (mo), days pregnant (d), and body condition score (BCS). Second, 30 mature range cattle were selected from the first trial and fitted with pedometers for 7 d to monitor activity with step counts and estimate distance traveled. Third, mature range cows (n = 25) selected from the first trial were fitted with global position system (GPS) collars, and placed on pinyon-juniper rangeland from 20 June 2014 to 17 September 2014. Forth, mature range cows (n = 28) were fitted with GPS collars, and placed on ponderosa pine rangeland from 17 September 2014 to 15 October 2014. Distance traveled, slope, distance from water, elevation data were collected from both GPS trials. Low-intake and high-intake cows consumed 9.3 and 12.2 kg/d, respectively (P < 0.0001). Low-intake cattle became pregnant sooner (P = 0.002) than high-intake cattle (average of 16 d sooner). Cattle age (mo) equaled 90 and 98 for low- and high-intake cows, respectively (P = 0.04). Weight, predicted DMI, and BCS did not differ between groups (P > 0.06). Step counts for low- and high-intake animals were 5839 and 5383 ± 2089, respectively (P = 0.61), and estimated distance traveled was 4.31 and 5.35 ± 1.66 km d⁻¹ for low- and high-intake animals, respectively (P = 0.77). Low-intake cows (6.23 km d⁻¹) traveled farther (P = 0.005) each day than high-intake cows (5.84 km d⁻¹) on pinyon-juniper rangelands, and high-intake cows utilized (P = 0.013) steeper slopes. No differences were detected (P ≥ 0.06) for distance traveled, distance from water, and elevation for cows grazing ponderosa pine rangeland). However, low-intake cattle preferred (P = 0.046) steeper slopes on ponderosa pine rangeland than high-intake cattle. These results indicate that low-intake animals may travel farther on some rangelands and rebreed earlier. Study Two - Commercial grade heifers (n = 173) born and raised on the University of Arizona's V bar V Ranch from 2012 to 2014 were fitted with radio frequency identification tags (RFID) and placed in a drylot equipped with Growsafe® technology (8 bunks) for 60 d in 3 groups based on birth year in order to calculate DMI, residual feed intake (RFI), ADG, G:F, and residual gain (RG). Birth date, birth weight, weaning weight, age at start of trial, initial trial weight, and final trial weights were also recorded. Residual feed intake scores were utilized to place heifers in one of three treatment groups, low-, medium-, and high-intake. Reproductive and calf data were collected on heifers born in 2012. Means for birth date, birth weight, weaning weight, initial weight, final weight, and ADG did not differ among the three treatments. Residual gain for low-, medium-, and high-intake heifers were different (P < 0.05) at 0.07, 0.00, and -0.07 kg d⁻¹, respectively. Low-intake cattle had an improved (P < 0.05) GF ratio of 0.19 when compared to the medium- and high-intake heifers with ratios of 0.15 and 0.13 (P > 0.05), respectively. Differences (P <0. 05) in DMI were detected with low-, medium, and high-intake heifers consuming 5.2, 6.2, and 7.5 kg d⁻¹, respectively. No differences were detected for pregnancy rate, calving rate, percent bred artificial insemination (AI), percent bull calves, calf birth weight, and calf birth date among treatments (P > 0.05).Study Three - Commercially available GPS tracking collars for cattle are cost prohibitive to most researchers. This paper will present a low-cost alternative to those collars (Knight GPS tracking collars), and provide detailed instructions on where to source materials and how to fabricate inexpensive GPS tracking collars. In addition, the two types of collars will be compared in a study where Brangus cattle (n = 8) were each fitted with LOTEK® 3300 and Knight GPS tracking collars for 31 d beginning 14 March 2015 at the Chihuahuan Desert Rangeland Research Center (CDRRC) 37 km north of Las Cruces, New Mexico. Location, slope, distance from water, distance traveled and elevation were recorded every 10 min. A record of GPS fix rate was logged. No differences were detected (P≥0.369) between collar types for location, slope, or distance from water. However, there was a tendency (P = 0.08) for Knight collars to report a lower estimate for distance traveled at 6171 m d⁻¹ compared to Lotek collars at 7104 m d⁻¹. Fix rate was greater (P≤0.001) for Lotek collars compared to Knight collars at 99.9 and 66.2%, respectively. Study Four - Previously characterized commercial cows (n = 26) were placed into either high (positive RFI) or low intake (negative RFI) groups. On 14 May 2015, 13 high- and 13 low-intake cows were fitted with modified igotU GT-120® GPS logging collars. Cattle were then placed on rangeland for 120 d. The first 30 d period animals transitioned from desert shrubland to pinyon-juniper. From 31 to 60 d, animals grazed pinyon-juniper rangeland. Next, during days 61 to 90, animals transitioned from pinyon-juniper to ponderosa pine, and the last 30 d were spent in ponderosa pine. Time periods will be referred to as month 1, 2, 3, and 4 for days 0 to 30, 31 to 60, 61 to 90, and 91 to 120, respectively. Location, slope, distance from water, elevation, and time spent close to water were recorded every 10 min. No differences were observed in the utilization of elevation or distance traveled, or distance from water (P>0.05). Low intake animals used a higher maximum slope (P < 0.05) during month 3, but slope utilization differences were not detected for other portions of the trial (P > 0.05). Study Five - Hereford sires (n = 35) with 7 or more cow offspring on the University of Arizona V bar V ranch in Rimrock, Arizona were tested at Neogen laboratories in Lincoln, NE for an Igenity Gold genetic profile. Their residual feed intake (RFI), ADG, tenderness, marbling score, milk production percent choice, yield grade, fat thickness, ribeye area, heifer pregnancy rate, stayability, maternal calving ease, birthweight and docility were estimated. Sires were given a genetic RFI score based on their RFI profile and placed into one of three intake groups, low (< 0.5 SD), medium (± 0.5 SD) and high (> 0.5 SD). Performance traits of cow offspring (n = 839) from those sires were also compared based on their sire's intake group. No differences (P > 0.05) were detected among sire intake groups for ADG, tenderness, marbling score, percent choice, yield grade, fat thickness, ribeye area, heifer pregnancy rate, stayability, maternal calving ease, birthweight and docility. Residual feed intake differed among groups (P < 0.05), and high intake cattle had more estimated milk production compared to low intake animals (P < 0.05). Cows from low intake sires were born later in the year (P < 0.05). High intake cattle had a higher (P < 0.05) birthweight and survived longer (P < 0.05) in the herd when compared to low and medium intake cows. Genetic RFI and expected milk production were moderately to highly correlated.

O presente trabalho teve por objetivo investigar a variação na secreção de LH em resposta ao tratamento com neurotransmissores, na presença ou não de esteróides gonadais e desta forma gerar informações sobre os mecanismos neuroendócrinos envolvidos na maturação sexual de novilhas da raça Nelore. A concentração de LH foi quantificada por radioimunoensaio e as novilhas ovariectomizadas (OVX) apresentaram maior concentração basal de LH (P&le;0,05), que as novilhas inteiras (INT). A administração de um antagonista gabaérgico (picrotoxina, 0,18 mg/kg, iv, amostras 15 min por 10 h) aos 8, 10, 14 e 17 meses de idade, aumentou (P&le;0,05) a concentração média e área total de secreção de LH nas novilhas INT tratadas aos 14 meses, a área total dos picos e área do maior pico de secreção de LH foi maior (P&le;0,05) nas novilhas OVX aos 14 e 17 meses de idade . A administração de um antagonista dopaminérgico (sulpiride, 0,59 mg/kg, sc, amostras 15 min por 10 h) aos 8, 12 e 16 meses de idade diminuiu (P&le;0,05) a secreção de LH (concentração média, área total, área total dos picos e área do maior pico secreção de LH) nas novilhas OVX aos 8 meses de idade. A administração de um estimulador alfa-adrenérgico (clonidina, 10 µg/kg, iv, amostras 15 min por 4 h) aos 8, 12 e 15 meses de idade, diminuiu (P&le;0,05) o número de picos nas novilhas OVX com 8 meses de idade. A administração do 17&beta;-estradiol (2 µg/kg, iv, amostra 15 min por 3 h, 1 h por 7 h e 3 h por 22 h) aos 10, 13 e 17 meses de idade diminuiu a diferença (P&ge;0,05) entre os grupos OVX e INT em relação ao número de picos, área total de picos, área do maior pico e tempo necessário para acontecer o maior pico. Foi avaliada a secreção de LH da desmama à primeira ovulação em novilhas INT e OVX. A concentração de LH aumentou durante a maturação sexual, tanto nas novilhas INT quanto nas OVX. O número de picos de secreção de LH e amplitude máxima de secreção de LH foi maior (P&le;0,05) nas novilhas OVX com o aproximar da primeira ovulação. Os resultados indicam uma diminuição da sensibilidade do hipotálamo aos esteróides gonadais durante o processo de maturação sexual nas novilhas da raça Nelore e a participação alternada de neurotransmissores, inibindo e estimulando a secreção de LH. Concluímos que, em novilhas pré-púberes da raça Nelore o desenvolvimento da retroalimentação positiva aos esteróides gonadais no hipotálamo foi importante para aumentar a secreção de LH antes da primeira ovulação, com a participação de neurotransmissores estimulando ou inibindo a secreção de LH. / The variation on LH secretion after neurotransmitter administration, on the presence or absence of gonadal steroid, was investigated, generating information about the mechanisms evolved on sexual maturation in Nellore heifers. LH concentration was quantified by RIA. As expected ovariectomized heifers higher basal LH concentration (P&le;0,05) than intact heifers. The picrotoxin administration (GABA antagonist, 0,18 mg/kg, iv, samples 15 min for 10 h) at 8, 10, 14 and 17 months of age increased (P&le;0,05) average concentration and total secretion area on intact treated heifers at 14 months and peak total area and area of highest peal on ovariectomized heifers at 14 and 17 months of age. The dopaminergic antagonist (sulpiride, 0.59 mg/kg, sc, sample 15 min for 10 h) administrated at 8, 12 and 16 months of age decreased (P&le;0,05) LH secretion (average levels, total peak area and area of the highest secretion peak) on ovariectomized heifers at 8 months of age. The administration of an alfa-adrenérgic stimulatory (clonidine 10 µg/kg, iv, samples 15 min for 4 h) at 8, 12 and 15 months of age decreased (P&le;0,05) decreased the number of peaks at 8 months of age. 17&beta;-estradiol administration (2 µg/kg, iv, samples every 15 min for 3 h, every 1 h for 7 h and every 3 h for 22 h) decreased the differences between ovariectomized and intact heifers on number of peaks, total peak area, highest peak area and time to highest peak occurrence. The LH secretion from weaning to first ovulation in non treated intact and ovariectomized heifers was also evaluated. LH concentration increase during sexual maturation in both ovariectomized and intact heifers. The number of peaks, and maximum LH secretion amplitude was higher in ovariectomized heifer closest to first ovulation, when compared to intact heifers. The results suggested a decrease on hipothalamus sensitivity to gonadal steroid during the sexual maturation in Nelore heifer associated with neurotransmitter participation either stimulating or inhibiting LH secretion. It was possible to conclude that the decrease of negative feedback associated with the increase on positive feedback of gonadal steroids over hipothalamus was necessary to increase LH secretion before first ovulation, that was associated with neurotransmitter participation on LH secretion.

Avaliou-se a influência do desenvolvimento corporal na ciclicidade, na resposta ovariana e na taxa de prenhez à inseminação artificial em tempo fixo (IATF) de novilhas da raça Nelore ao sobreano (Experimento 1). Ainda, avaliou-se a eficiência de um protocolo de indução de ciclicidade (Experimento 2) previamente ao protocolo de IATF. No Experimento 1, 650 novilhas de 13,9&#177;0,03 meses de idade foram submetidas ao mesmo protocolo de sincronização da ovulação para IATF. Dez dias antes do início do protocolo de sincronização (Dia -10), as novilhas foram avaliadas quanto à idade (meses), peso (kg), escore de condição corporal (ECC, escala de 1 a 5), altura de cernelha (hCERN, cm) e relação altura/profundidade de costela (pCOST,% ) escore do trato reprodutivo (ETR, escala de 1 a 5), ciclicidade (presença de CL) e espessura de gordura subcutânea na garupa (EGPU, mm). No Dia 0, as fêmeas foram submetidas a sincronização da ovulação, recebendo IATF 10 dias após (Dia 10). Foram determinados por ultrassonografia a taxa de ciclicidade (presença de CL no Dia -10 e/ou Dia 0) os diâmetros do maior folículo presente no Dia 8 (FDD8), no Dia 10 (FDIA), presença de CL no Dia 17 (ovulação) e taxa de prenhez 30 dias após a IATF. Com relação à análise univariável, não houve diferença na taxa de ciclicidade com relação à hCERN e pCOST (P&gt;0,05), mas isoladamente a idade, o peso, o ECC e a EGPU foram associados com incremento na taxa de ciclicidade (P&lt;0,05). Entretanto, na análise multivariável o parâmetro retido no modelo foi a EGPU (&gt;3,4mm; 19,4 vs. &le;3,4mm; 8,8%; P=0,002). O FDD8 não foi influenciado pela idade, ECC e pCOST (P&gt;0,05) quando analisados de maneira isolada. Entretanto, o peso, hCERN, EGPU e ETR foram associados com maior FDD8 (P&lt;0,05). Contudo, ao se avaliar todos os parâmetros de maneira conjunta, houve efeito de hCERN (&gt;121,5=7,2 vs. &le;121,5=6,9mm; P=0,03), EGPU (&gt;2,6=7,4 vs. &le;2,6=6mm; P=0,02) e ETR (1=6,9ab;2=7,4ab; 3=7,1ab; 4=7,7ª; 5=6,3mmb; P=0,002) sobre o FDD8. O CrescFD e a taxa de ovulação não foram influenciados por nenhum dos parâmetros avaliados, em ambas as análises (P&gt;0,05). Ainda, na análise univariável a hCERN e o ETR (P&gt;0,05) não resultaram em efeito na taxa de prenhez, mas a idade, o peso, o ECC, a pCOST e a EGPU foram associados com incremento no sucesso gestacional (P&lt;0,01). Entretanto, ao se utilizar a análise multivariável os parâmetros retidos no modelo foram a idade (&gt;13,8=43,0 vs. &le;13,8=27,2; P=0,04), a pCOST (&gt;44,0=41,9 vs. &le;44,0=27,0; P = 0,02) e a EGPU (>2,5=44,4 vs. &le;2,5=23,4%; P=0,0003). No Experimento 2, 626 novilhas de 14,2±0,03 meses de idade foram aleatoriamente distribuídas em dois grupos experimentais: Indução (n=307; dispositivo de P4 usado durante 10 dias mais 0.6mg de CE no momento da retirada) e Controle (n=319). Doze dias após a retirada do dispositivo de P4 (Dia 0) todas as fêmeas foram submetidas a protocolo de sincronização para IATF conforme descrito no Experimento 1. As novilhas que receberam o protocolo de indução tiveram maior (P<0,0001) taxa de ciclicidade (75,2%) no Dia 0 em relação ao controle (7,8%). Entretanto, semelhante taxa de prenhez à IATF foi verificada entre os tratamentos (Controle 42,9 vs. Indução = 43,0%; P=0,40). Conclui-se que os parâmetros de desenvolvimento corporal apresentam relação positiva com a ciclicidade e a resposta ao protocolo para IATF em novilhas raça Nelore ao sobreano. Além disso, o estímulo hormonal prévio aumentou a proporção de novilhas com CL no início do protocolo de IATF, entretanto, não influenciou a taxa de prenhez à inseminação artificial / The influence of body development on ciclicity, ovarian response and pregnancy rate after timed artificial insemination (TAI) was evaluated in yearling Nelore beef heifers (Experiment 1). Furthermore, the efficiency of a protocol for ciclicity induction, previously to the TAI was tested (Experiment 2). At Experiment 1, 650 heifers aged 13,9 ± 0.03 months were submitted to the same ovulation synchronization protocol for TAI. Ten days before the beginning of the TAI protocol (Day -10), all females were evaluated for age (months), weight (kg), body condition score (BCS, 1 to 5 scale), withers height (hCERN, cm) and whiters height/depth of rib relationship (pCOST, %), reproductive tract score (RTS, 1 to 5 scale) ciclicity (presence of a CL) and subcutaneuos fat thickness (EGPU, mm). At Day 0, all heifers were submitted to the ovulation synchronization, receiving TAI after 10 days (Day 10). The ciclicity (presence of a CL at Day -10 and/or Day 0), diameter of the biggest follicle at Day 8 (FDD8) and Day 10 (FDIA) as the ovulation rate at Day 17 and pregnancy rate at Day 30 were determined by ultrassonography. In relationship to the univariable analysis, there was no difference of ciclicity rate according to hCERN and pCOST (P>0.05), but age, weight, BCS, and EGPU were associated to greater ciclicity (P<0.05). However, considering the multivariable analysis, heifers with greater EGPU (>3.4mm; 19.4%) presented greater (P=0.002) ciclicity rate in comparison to heifers with lesser EGPU ( &le;3.4mm; 8.8%). The FDD8 was not influenced by age, BCS and pCOST (P>0.05) and was influenced by hCERN, EGPU and RTS when the variables were singly analyzed. Nevertheless, there was an effect of hCERN (>121.5=7.2 vs. &le;121.5=6.9; P=0.03), EGPU (>2.6=7.4 vs. &le;2.6=6.0; P=0.02) and RTS (1=6.9ab; 2=7.4ab; 3=7.1ab; 4=7.7ª; 5=6.3 mmb; P=0.002) over the FDD8, when all variables were analyzed together. The ovulation rate was not influenced by any of the evaluated parameters (P>0.20). Still, considering the univariable statistical model, there was no effect of hCERN and RTS (P=0.05) on pregnancy rate, but age, weight, BCS, pCOST and EGPU were associated with increased pregnancy rate to TAI (P<0.05). Still, heifers with more age (>13.8=43.0 vs. &le;13.8=27.2; P=0.04), greater pCOST (>44.0=41.9 vs. &le;44.0=27.0%; P = 0.02) and greater EGPU (>2.5=44.4 vs.&le;2.5mm=23.4%; P=0.0003) presented greater pregnancy rate when all varaiables were analyzed together. At Experiment 2, 626 heifers aged 14.2±0.03 months were randomly allocated in two experimental groups: Induction (n=307; used P4 device during 10 days plus 0.6mg EC at device removal) and Control (n=319). Twelve days after P4 device removal (Day 0) all females were submitted to the same ovulation synchronization protocol described in Experiment 1. Heifers from Induction group (75.2%) had greater (P<0.0001) ciclicity rate at Day 0 in comparison to Control (7.8%), but similar pregnancy rate to 1st TAI (Control 42.9 vs. Induction 43.0%; P=0.40). It is concluded that the body developmental parameters presents positive relationship with ciclicity and response to the TAI protocol in Nelore yearling heifers. Moreover, a previous hormonal stimulus increases the proportion of heifers with a corpus luteum at the beginning of the TAI protocol, but does not affect pregnancy rate to the artificial insemination

Rearing heifers is one of the most important activities undertaken in the framework of the operation of dairy cattle farms. Corn silage and perennial forage crops are an important feed for livestock. During their production is important to follow all technological procedures starting from the selection of seed forage crops to quality covering the silo. Failure to observe technological processes leads to problems of poor fermentation process which results in poor feed, which immediately reflected on the animals. The aim of this thesis was to evaluate nutritive value of silages. The literature review processes the nutrition of the heifers in the agricultural cooperative Zemědělská Klučenice, a.s. It includes also the composition of the feed ration, the share of individual components and their nutrient composition. Agricultural cooperative owns modern technology. The result there were no deficiencies in feed rations and in hygiene. In the conclusion, the author suggests possible solutions improve.