Mammary gland samples from a large serial-slaughter Holstein heifer nutrition trial were used to determine the effects of stage of development and nutritional management on mitogenic activity of mammary extracts and mammary parenchymal composition. Stage of development and nutritional management of heifers had minimal effects on the mitogenic capacity of mammary extracts, and no significant effects on tissue composition. Two-dimensional proteome maps of heifer mammary extracts were constructed for heifers weighing 200 and 350 kg, respectively at slaughter. Proteins altered by stage of development and/or nutrition were quantified and identified; 820 total protein spots were analyzed. The expression of 131 protein spots differed by dietary treatment only. Stage of development altered the expression of 108 protein spots. Twenty-two protein spots were excised from gels for mass spectrometry analyses. Database searches for proteins with shared primary amino acid sequences were used to identify the proteins. Possible roles of these proteins in mammary development were described. In summary, heifers can be reared on high planes of nutrition without impairing mammary development, but mechanisms governing nutritional and temporal control of mammary development demand further investigation. / Master of Science

Ovarian secretions and growth hormone (GH) are major endocrine regulators of mammary growth and development in bovine mammary gland; but information on endocrine regulation during early prepubertal period is limited. Our overall objective was to study the regulation of mammary growth and development as well as transcript abundance in early prepubertal bovine mammary gland by ovarian secretions and exogenous bovine somatotropin (bST). In the first study, we determined the effect of staged ovariectomy on mammary growth and development in two to four month old Holstein heifers. In the second study, effects of bST on mammary growth and development, and also on putative stem cell population were evaluated by beginning bST treatment in one month old Holstein heifers. Mammary growth and development was determined by mass of mammary tissue, biochemical analyses, histological examination, transcript abundance and protein expression in mammary parenchyma (PAR) and fat pad (MFP). Ovariectomy reduced mass and lipid content of PAR without affecting the histological characteristics or rate of epithelial cell proliferation. There was a marked reduction in progesterone receptor expression both at the mRNA and protein level. Ovariectomy also reduced transcript abundance in GH receptor (R), insulin-like growth factor (IGF)-1, IGF binding protein -6, estrogen responsive and proliferation marker genes, but increased the mRNA abundance of IGF-1R in PAR. On the other hand, administration of bST did not have an impact on PAR growth, epithelial proliferation, putative stem cell population or transcript abundance of IGF-axis genes. However, bST reduced the relative abundance of GHR, signal transducers and activators of transcription-5b and suppressors of cytokine signaling-2 in mammary PAR. Transcript abundance of IGF-axis molecules, estrogen responsive genes and proliferation markers in MFP was not affected by ovariectomy or bST. Overall, our data suggest that ovary is a predominant regulator of mammary growth and development in prepubertal heifers and that exogenous bST is not effective as a mammary specific mitogen in very young prepubertal heifers. / Ph. D.

Recent efforts have improved synchronization systems that facilitate timed insemination in beef cattle. However, synchronization systems utilizing a single fixed-time artificial insemination (FTAI) frequently result in 25-40% non-pregnant heifers. The purpose of this study was to determine the effectiveness and define economic parameters of a FTAI resynchronization protocol in beef heifers after synchronization using a 5d CO-Synch + CIDR system. Estrus was synchronized in crossbred heifers (n=176) using 5 d CO-Synch + CIDR with FTAI at 72 h. After the initial AI, open heifers received either resynchronization (RS) or natural service (NS) return service treatments. The RS treatment was diagnosed for pregnancy 29 d after the initial AI, and all open heifers were resynchronized using the 5 d CO-Synch + CIDR with FTAI at 72 h. Heifers diagnosed pregnant following initial AI received no further treatment. Heifers in the NS treatment were exposed to fertile bulls from d 14 to d 66 following initial AI. Return to estrus data were collected using the Heat Watch Estrus Alert System. Total AI pregnancies tended to be higher (P=0.07) for RS (69.7%) than NS (56.5%) heifers. Overall pregnancy rate was greater for NS (89.4%) than for RS (69.7%) at the end of the breeding season (P < 0.01). The cost of RS was $128.63 and for NS was $82.50 per pregnancy. The expected average calf value per heifer exposed was $195.84 for RS treatment and $357.62 for NS treatment. This difference was attributed to the increased number of open heifers in the RS treatment. The resynchronization of estrus after the initial FTAI yielded a limited number of pregnancies in the breeding season in this study. However, the resynchronization program also cost more per pregnancy. Further investigation into resynchronization should focus on both biological and economic impacts. / Master of Science

Two studies were conducted to assess factors affecting estrogen excretion in dairy heifers. The objective of the first study was to quantify estrogenic activity in feces and urine during the estrous cycle. Ten non-pregnant Holstein heifers were fed the same diet for 28 d. Plasma, feces, and urine samples were collected daily. Plasma 17-β estradiol (17-β E2) was quantified with RIA and used to confirm day of estrous. Feces and urine samples from days -12, -6, -2, -1, 0, 1, 2, 6, 12 of the estrous cycle were analyzed with RIA and Yeast Estrogen Screen (YES) bioassay. Plasma 17-β E2 concentrations peaked on day of estrus, with feces and urine estrogenic excretion peaking a day after. The objective of the second study was to quantify variation in estrogenic activity in feces and urine due to increased dietary phytoestrogen content. Ten Holstein heifers were randomly assigned to treatment sequence in a two-period crossover design. Dietary treatments consisted of grass or red clover hay, and necessary supplements. Feces and urine samples were collected and pooled for analysis. Estrogenic activities of pooled samples were quantified using the YES bioassay. Estrogenic excretion in feces and urine was higher for heifers fed red clover hay. Fecal and urine samples from five heifers were analyzed using LC/MS/MS to quantify excretion of phytoestrogenic compounds. Heifers fed red clover hay excreted more equol than heifers fed grass. Identifying sources of variation in estrogenic activity of manure will aid in the development of practices to reduce environmental estrogen accumulation. / Master of Science

Master of Science / Department of Animal Sciences and Industry / Karol E. Fike / David M. Grieger / Synchronizing estrus before AI is an effective way to shorten the breeding season, and increasing the number of pregnancies per AI may lead to greater use and acceptance of synchronization protocols among beef producers. Our objective was to determine if pregnancy rates to fixed-time AI (FTAI) would be improved by delaying insemination in heifers not expressing estrus before FTAI in a 7-d CO-Synch + controlled internal drug release (CIDR) estrus-synchronization protocol. In Experiment 1, yearling beef heifers (n = 465) at three locations of commercial and purebred herds were treated with GnRH (Cystorelin 100 µg im) and a CIDR insert (1.38 g of progesterone) on Day 0. On Day 7 CIDR inserts were removed and all heifers received PGF[subscript]2α (Lutalyse 25 mg im) and were fitted with an estrus-detection patch (Estrotect; Rockway, Inc.). Heifers were assigned to three treatments based on estrus-detection patch color at 48 h after PGF[subscript]2α: (1). Estrus-Red 48 h (Red 48; n = 180), heifers that expressed estrus and were inseminated at 48 h; (2). Non-Estrus-Gray 48 h (Gray 48; n = 137) heifers that did not express estrus and were inseminated at 48 h; and (3). Non-Estrus Delayed- 56 h (Gray 56; n = 148), heifers that did not express estrus at 48 h, and were not inseminated until 56 h after PGF[subscript]2α. Pregnancy rate to AI was greatest (P < 0.0001) for Red 48 heifers (67.8%) compared with heifers in the Gray 48 (39.4%) and Gray 56 (42.6%) treatments. Heifers assigned to Gray 48 and Gray 56 achieved similar (P = 0.83) pregnancy rates. In Experiment 2, yearling beef heifers (n = 257) at two different locations were treated with the same 7-d CO-Synch protocol, but heifers were assigned to three different treatments based on estrus-detection patch color at 48 h after PGF[subscript]2α: (1). Estrus-Red 48 h (Red 48; n =95), heifers that expressed estrus and were inseminated at 48 h; (2). Non-Estrus-Gray 48 h (Gray 48; n = 84), heifers that did not express estrus but were inseminated at 48 h; and (3). Non-Estrus Delayed- 72 h (Gray 72; n = 78), heifers that did not express estrus at 48 h, and were not inseminated until 72 h after PGF[subscript]2α. Pregnancy rate to AI was greatest (P = 0.004) for Red 48 heifers (62.1%) compared with heifers in Gray 48 (40.5%), and Gray 72 (46.2%). No difference in pregnancy rates (P = 0.75) was detected between heifers assigned to treatments Gray 48 and Gray 72. Delaying insemination in heifers not expressing estrus by 48 h after PGF[subscript]2α did not improve pregnancy rates to AI.

Made available in DSpace on 2015-03-26T13:55:27Z (GMT). No. of bitstreams: 1 texto completo.pdf: 1221386 bytes, checksum: 1fdc7f75942a2e0b2d9d372d963168c7 (MD5) Previous issue date: 2014-06-30 / The purpose of this study was to determine the feasibility productive, carcass characteristics and meat quality of heifers finished in grazing with supplementation and slaughtered at three different times. The first part comprise a literature review of aspects of beef production in Brazil, as well the importance of the production of meat with females and their implications on performance, carcass quality and meat. The second part aimed evaluate the performance, carcass characteristics and meat quality of three different genotypes heifers finished on pasture / supplement system and slaughtered in three times of supplementation. To achieve this goal, were finished on pasture with supplementation of 0.7% of body weight, heifers from three genetic groups: Angus X Nelore (ANE); Mixed Dairy (MLT) and Nelore (NEL), being 36 heifers ANE, 32 MLT e 30 NEL, with initial body weight of 267+23; 305+31; and 320+19 kg respectively. Heifers were grouped into seven homogeneous lots, slaughtered a batch of 18 heifers (6 of each genetic group) to start the experiment as slaughter reference that was used to calculate the empty body weight and carcass weight of the original animals that remained in the experiment. The slaughter was carried out in a commercial refrigerator. The remaining heifers were grouped into homogeneous lots with the same number of animals of each genetic group. These lots were placed in continuous grazing providing daily multiple supplementation to 0.7% of the lots weight. The animals were weighed every 28 days to adjust the amount of supplement offered and determine performance. Likewise, every 28 days was collecting pasture by means of the technique of double sampling to determine the availability and morphological composition of pasture in the paddocks, while pasture sampling was performed by simulated grazing to determine forage quality. Three experimental slaughter was carried out, the first 60 days of supplementation with 26 heifers slaughtered (10 ANE, 8 MLT and 8 NEL), the second at 90 days shooting 26 heifers (10 ANE, 8 MLT and 8 NEL) and the last to 132 days with 28 animals (10 ANE, 10 MLT and 8 NEL). In all slaughtering, the carcass components and not carcass were weighed to determine the empty body weight and carcass yield based on body weight and empty body weight. At the end of the slaughter line, the carcass was divided into two equal parts and placed in the cooling chamber. After 24 hours in the chamber, temperature and final pH were measured, and weighed again to determine the carcass weight of the cold carcass. The difference between hot carcass weight hot and carcass weight cold generate a chilling losses. The carcass right was separated into Front, Rear and Tip Needle cuts, these parts being weighed to determine the percentage based on the weight of the hot carcass. The same half carcass right, were obtained six steaks of 2.5 cm thick of Longissimus dorsi were divided into three groups of two steaks each, and placed to mature for 0, 7 and 14 days each group. These steaks were used to determine the quality of the meat, analysis of cooking losses, color, shear force, sarcomere length and myofibrillar fragmentation index being performed. On the other hand, the half carcass left was obtained section between the 9th and 11th ribs (section HH) to determine the chemical composition of the carcass and empty body by means of the equations proposed by BR-CORTE (2006). For the statistical analysis of the performance and carcass characteristics of an experimental randomized design with factorial arrangement 3x3, with the MIXED procedure of SAS, version 9.2 (SAS, 2008) using the initial weight as a covariate was used. As for the quality of the meat, the data were analyzed as repeated measures in function of ripening time (0, 7 and 14 days). Comparisons between means were performed using the test "t" at the level of 10% probability. The results showed a half production of the forage of 6.78 t/DM/ha, with 32% of green leaves and 26% of dead leaves, however the half of MSPD was 5.06 t/MSpd/ha. The pasture had 7.53% crude protein and 67.21% of FDNcp. Animal performance was interaction between time of supplementation and genetic group for the final weight, average daily gain, carcass weight hot, gain in carcass weight, carcass weight cold and percentage of the back cut. The ANE heifers had the highest final weight and average daily gain increased (P <0.1). The weight of hot and cold carcass, the ANE and NEL heifers showed higher value, differing from MLT that had lower (P <0.1). Carcass yield based on the body weight, the NEL heifers had 54% yield surpassing the ANE and MLT (P <0.1) with 52% yield. Likewise, the NEL heifers had the best performance gain of 68%, outperforming the ANE (61%) and MLT (54%), being different among the three genotypes (P <0.1). The initial and final temperature and pH did not differ between genetic groups. While the carcass cuts, the ANE heifers had the highest percentage of rear with 50.9% (P <0.1), surpassing the MLT and NEL with 50.3 and 50% respectively, no finding difference between them. Concludes that termination of heifers on pasture/supplement system is a viable option to increase the production of beef, and crossbred and Nelore females are available, in addition to presenting good carcass conformation and good yield rear; however, the shear force presented by the meat was high, which decreases the quality. / A proposta deste trabalho foi determinar a viabilidade produtiva, características da carcaça e qualidade da carne de novilhas terminadas em pastejo com suplementação e abatidas a três diferentes tempos. A primeira parte compreende uma revisão bibliográfica dos aspectos de produção de carne bovina no Brasil, assim como a importância da produção de carne com fêmeas e seus implicações sobre o desempenho, qualidade da carcaça e da carne. Na segunda parte, objetivou-se avaliar o desempenho, características da carcaça e qualidade da carne de novilhas de três diferentes genótipos terminadas no sistema pasto/suplemento e abatidas em três tempos de suplementação. Para lograr este objetivo, foram terminadas em pastejo com suplementação múltipla a 0,7% do peso corporal, novilhas de três grupos genéticos: 1&#8260;2 Angus X 1&#8260;2 Nelore (ANE); Mestiça Leiteira (MLT) e Nelore (NEL), sendo 36 novilhas ANE, 32 MLT, e 30 NEL, com peso corporal inicial de 267+23; 305+31; e 320+19 kg respectivamente. As novilhas foram agrupadas em sete lotes, sendo abatido um lote de 18 novilhas (6 de cada grupo genético) ao início do experimento como abate referência que utilizou- se para calcular o peso do corpo vazio e peso da carcaça inicial do animais que continuaram no experimento. Os abates foram realizados em frigorífico comercial. As novilhas restantes foram agrupadas em lotes homogêneos com a mesma quantidade de animais de cada grupo genético. Estes lotes foram colocados em pastejo continuo fornecendo diariamente suplementação múltipla a 0,7% do peso corporal do lote. Os animais foram pesados a cada 28 dias para ajustar a quantidade de suplemento oferecido e determinar o desempenho. Assim mesmo, a cada 28 dias foi realizada coleta de pasto por médio da técnica de dupla amostragem para determinar a disponibilidade e composição morfológica do pasto nos piquetes, ao mesmo tempo, foi realizada amostragem do pasto por pastejo simulado para determinar a qualidade da forragem. Foram realizados três abates experimentais, o primeiro aos 60 dias de suplementação sendo abatidas 26 novilhas (10 ANE, 8 MLT e 8 NEL), o segundo aos 90 dias abatendo 26 novilhas (10 ANE, 8 MLT e 8 NEL) e o último aos 132 dias com 28 animais (10 ANE, 10 MLT e 8 NEL). Em todos os abates foram pesados os componentes carcaça e não carcaça dos animais para determinar o peso do corpo vazio e rendimento de carcaça em base ao peso corporal e peso do corpo vazio. Ao final da linha de abate, a carcaça foi dividida em duas partes iguais e colocadas em câmara de resfriamento. Após 24 horas na câmara foram mensurados a temperatura e pH finais, além de pesar novamente a carcaça para determinar o peso da carcaça fria. A diferença entre o peso da carcaça quente e o peso da carcaça fria gero a quebra por resfriamento. A carcaça direita foi separada nos cortes Dianteiro, Traseiro e Ponta de Agulha, sendo estas partes pesadas para determinar a porcentagem em base ao peso da carcaça quente. Na mesma meia carcaça direita, foram obtidos seis bifes de 2,5 cm de espessura do músculo Longissimus dorsi, que foram divididos em três grupos de dois bifes cada, e colocados a maturar durante 0, 7 e 14 dias cada grupo. Estes bifes foram utilizados para determinar as características de qualidade da carne, sendo realizados analises de perdas por cocção, cor, força de cisalhamento, comprimento de sarcômero e índice de fragmentação miofibrilar. Por outro lado, da meia carcaça esquerda foi obtida a seção compreendida entre a 9°e 11°costelas (seção H-H) para determinar a composição química da carcaça e do corpo vazio por médio das equações propostas pelo BR-CORTE (2006). Para a análises estatístico do desempenho e características da carcaça foi utilizado um delineamento experimental inteiramente casualizado, com arranjo fatorial 3X3, com o procedimento MIXED do SAS, versão 9.2 (SAS, 2008), utilizando o peso inicial como covariável. Já para a qualidade da carne, os dados foram analisados como medidas repetidas no tempo, em função do tempo de maturação (0, 7 e 14 dias). As comparações de médias foram realizadas utilizando-se teste t a nível de 10% de probabilidade. Os resultados do forragem mostraram uma produção meia de 6,78 t/MS/ha, com 32% de folhas verdes e 26% de folhas mortas, entanto a MSpd meia foi de 5,06 t/MSpd/ha. O pasto apresentou 7,53% de proteína bruta e 67,21% de FDNcp. No desempenho animal houve interação entre tempo de suplementação e grupo genético para o peso final, ganho médio diário, peso da carcaça quente, ganho em carcaça, peso da carcaça fria, peso e porcentagem do corte traseiro. As novilhas ANE apresentaram o maior peso final e maior ganho médio diário (P<0,1). No peso da carcaça quente e fria, as novilhas ANE e NEL apresentaram valor mais alto, diferindo das MLT que apresentaram o menor valor (P<0,1). No rendimento de carcaça em base ao peso corporal, as novilhas NEL apresentaram 54% de rendimento superando as ANE e MLT (P<0,1) com 52% de rendimento. Da mesma forma, as novilhas NEL tiveram o melhor rendimento de ganho com 68%, superando as ANE (61%) e MLT (54%), sendo diferentes entre os três grupos genéticos (P<0,1). A temperatura e pH inicial e final não diferiram entre grupos genéticos. Enquanto aos cortes da carcaça, as novilhas ANE apresentaram a maior porcentagem de traseiro com 50,9% (P<0,1), superando as MLT e NEL com 50,3 e 50% respectivamente, não encontrando diferença entre estas. Se conclui que a terminação de novilhas no sistema pasto/suplemento é uma opção viável para elevar a produção de carne bovina, sendo que fêmeas mestiças e Nelore encontram-se disponíveis no mercado, além de apresentar à terminação boa conformação de carcaça e bom rendimento do traseiro; entretanto, a força de cisalhamento apresentada pela carne foi alta, o que diminui a qualidade.

This trial was conducted in two phases during the period of February 2002 – June 2003. In phase 1 of the study the growth potential of calves fed either commercial Surromel Calf® (CSM) or experimental Surromel Calf (ESM) without calf starter was evaluated. In phase 2 of the study calves were fed either experimental Surromel Calf (ESM) or full milk with starter. High production cost and the availability of new technology prompted Clover SA to investigate other processes of manufacturing Surromel Calf®. The implementation of a new manufacturing process however, also necessitates evaluation of the end product. Twenty four Holstein heifer calves were used in a completely randomized block design. Calves were liquid fed only. For the first two weeks the milk replacer was allocated at 10% of body weight (2l fed twice daily), from week 3 to week 6 at 12.5% of body weight (2.5l fed twice daily) and during week 7 and week 8 calves received the milk replacer at 15% of body weight (3l milk fed twice daily). Water was available ad lib except for 30 minutes before and after milk replacer feedings. Body weight and skeletal development (body length, shoulder height, shoulder width and chest diameter) were measured weekly. The fecal consistency was subjectively scored daily. Mean average daily gains were 170g/day and 176g/day for calves receiving either ESM or CSM respectively. No differences were observed between treatments (P>0.05) for any change in body stature measurements over the 56 day trial period. If a price-competitive milk replacer could guarantee similar growth results as full milk, then milk producers would have confidence in using these replacers instead of full milk. In phase 2 of the trial calves were fed either 2l of full milk (FMS) or experimental Surromel Calf (EMSS) twice daily from birth up to 56 days. Calves had ad lib access to a commercial calf starter. Starter consumption was negligible for the first three weeks. Starter intake was 0.30kg/d and 0.34kg/d respectively at 35 days of age and 1.11kg/d and 1.10kg/d for FMS and EMSS calves respectively at 56 days (P>0.05). The average daily gain (ADG) were 370g/day and was unaffected by treatment (P>0.05). No differences were observed between treatments (P>0.05) for any change in body stature measurements. Growth standards for dairy calves with body weight less than 100kg have been included for the first time in the NRC Dairy 2001. Many producers are reluctant to use these recommendations since these have not been validated under South African conditions. The growth prediction was only compared with the growth of calves in Phase 2. The results showed that the NRC growth predictions are in agreement from week 3 onwards with the current study‘s growth results. / Dissertation (MSc (Agric) : Animal Nutrition)--University of Pretoria, 2008. / Animal and Wildlife Sciences / unrestricted

The highly regulated maturation of the mammary gland is poorly understood. Our studies were designed to further characterize the role of ovarian hormones, growth hormone (GH)/IGF axis proteins and extracellular matrix (ECM) in the growth and development of prepubertal mammary glands. Prepubertal heifers were injected with either exogenous GH or subjected to ovariectomy (OVX). Mammary parenchyma (PAR) and mammary fat pad (MFP) were harvested for DNA, protein, lipid, and western blot analysis. Remaining tissues were preserved for histological staining or snap frozen for quantitative real-time PCR. We examined 13 genes that work in conjunction with the extracellular matrix to regulate mammary proliferation and morphogenesis. Administration of GH, while impacting composition of MFP, had no effect on expression of the selected genes; there was a decrease in expression of fibronectin in PAR. Ovariectomy had no effect on gene expression in MFP but decreased expression of epimorphin, a potent regulator of morphogenesis, in PAR. In both experiments, the presence of a 55 kDa band corresponding to androgen converting enzyme aromatase was detected but its expression was unaffected. In another study, we used in vitro cell culture to evaluate the role of ECM in mammary gland maturation and employed quantitative real-time PCR to evaluate gene expression profiles of select genes involved in proliferation and differentiation. Expression of Rac1 was decreased in response to bovine insulin (BI) but increased on collagen I (Col). Expression of aldehyde dehydrogenase was decreased in BI and serum on plastic and on Col in the presence of BI. Expression of IGF binding proteins (BP) 3, -4, and -6 were decreased in the presence of serum on laminin (LM). Also, IGF-BP2 expression was decreased on Col while IGF-BP6 was increased on LM with BI. Clusterin, a ubiquitous non-adhesive ECM protein was not affected by ECM substrate but did increase over time. In conclusion, we propose that the mammary gland is not able to respond to GH at this age and that while OVX did effect the expression of some genes, the presence of aromatase maintained local estrogen concentrations. Furthermore, ECM alone is insufficient to regulate mammary gland development and growth. / Ph. D.

Current data indicates that feeding dairy calves more nutrients in early life allows them to produce more milk in the future. Mechanisms responsible are poorly understood. Thirty-six Holstein heifer calves were fed either a restricted (R; 20.2% crude protein [CP], 19.8% fat, dry matter (DM) basis, fed at 0.44 kg/hd/d, DM basis) or an enhanced (EH; 28.9% CP, 26.2% fat, DM basis, fed at 1.08 kg/hd/day, DM basis) milk replacer (MR) and given either a placebo or estradiol (E2) implant to assess differential responses to E2. Our underlying hypothesis was that calves fed more nutrients are better able to respond to mammogenic stimuli and will have a more developed mammary gland as a result of imposed treatments. Enhanced-fed calves grew at a faster rate, were heavier at weaning, and had more functional mammary tissue (i. e., parenchyma; PAR) mass in the mammary gland at weaning (7.3-fold). Additionally, biochemical composition of the PAR was not impacted by the dietary treatments imposed. Furthermore, EH-fed calves had an increase in the number of actively dividing cells throughout the mammary PAR as well as increased intensity of estrogen receptor expression in the population of cells expressing the estrogen receptor. Enhanced-fed calves had an up-regulation of genes and pathways in the PAR related to metabolism, cellular signaling, and cellular growth. When given E2, EH-fed calves experienced the greatest overall mammary gland development and had the greatest PAR mass without compromised composition. When comparing EH- and R-fed calves given E2, differential expression of genes and pathways related to cell growth, cell signaling, and metabolism was observed. In summary, data indicates that enhanced feeding of calves in early life allows increased responsiveness to mammogenic stimuli and a corresponding increase in mammary development. We suggest that this may at least partly explain the improved future milk production in calves fed in this manner. / Ph. D.

No description available.