The objective of this study was to determine the onset of puberty by using progesterone profiles and anterior pituitary gonadotropin releasing hormone (GnRH) challenges in purebred and crossbred Holstein and Jersey heifers. In experiment 1, fifty prepubertal heifers by four sire - dam classifications (18 HH, 11 JJ, 10 JH, and 11 HJ) were used. The HH heifers attained puberty at an older age than the HJ, JH or JJ heifers, and these three classifications were not different from each other. There were significant differences in weight and wither height at puberty and average daily weight gain (ADWG) between all four sire - dam classifications. Season of birth had a significant effect on age and weight at puberty. In experiment 2, four prepubertal heifers from each sire - dam classification in experiment 1 were used at 3, 6, 9 and 12 mo of age to determine the effects of administering 200 μg GnRH on LH secretion. The effects of breed, age at challenge, and their interaction were only significant for time to LH peak. In conclusion, age at puberty in crossbred Holstein X Jersey heifers is regulated by breed and season of birth, and further research with larger sample sizes is needed to establish the relationship of pituitary maturation and the capacity to secrete LH in response to GnRH stimulation as related to onset of puberty in purebred and crossbred dairy heifers. / Master of Science

Made available in DSpace on 2016-12-08T16:24:11Z (GMT). No. of bitstreams: 1 PGCA10MA064.pdf: 877931 bytes, checksum: ef65c09f07dc6c43c6a132d5ed45fb8b (MD5) Previous issue date: 2010-08-19 / Holstein is the dominant breed in dairy herds in southern Brazil, being known by the high milk yield, with low solids concentration, reduced fertility and longevity and high proportion of dystocia. The crossing with other specialized dairy breeds, especially Jersey, has been utilized as an option to reduce the deficiencies of the Holstein. The aim of this study was to evaluate dystocia in Holstein cows inseminated with Holstein or Jersey and performance of the calves resulted from these matings (growth, immune status and prevalence of diarrhea in the first days of life). The study was conducted at the Centro de Ciências Agroveterinárias of the Universidade do Estado de Santa Catarina (UDESC) in Lages, SC, Brazil. Forty cows and heifers were randomly inseminated with Holstein or Jersey, leading to the birth of 23 Holstein calves (11 males and 12 females) and 17 crossbred calves (7 males and 10 females). The birth were observed and a scale for calving ease from 1 (easy, unassisted) and 5 (extreme difficulty) were used. After birth, calves were housed in individual pens weight, height at withers, chest diameter and diameter and length of the head were obtained, and these measures were weekly repeated. Until one hour after birth, calves fed 2 liters of colostrum, and a second dose within 8 hours. In the following two days, they received 4 liters / day of transition milk, from the 4th day began to receive 4 liters / day of whole milk and starter concentrate. On day 42, calves were weaned and the diet was based in starter concentrate added to 20% alfalfa hay. Daily supply and plenty of concentrate were weighed and fecal score assigned on a scale from 1 (normal faeces) to 4 (fluid faeces). The samples of blood serum proceeded soon after birth, with 24 hours, 15, 30, 42, 49 and 84 days of age to assess the immunity of calves. Dystocia were observed only in Holstein calves (17.39%). The F1 Holstein x Jersey had lower weight and height at birth (35.2 kg and 72 cm) compared to the Holstein straigthbred (42.8 kg and 76.3 cm) at weaning and at the end of the experiment (84 days old), with no difference in weight gain and height growth (P> 0.05). There was no difference between genetic groups in concentrate intake and feed conversion. F1 calves have higher levels of protein and immunoglobulins in blood serum with 24 hours and 15 days of age, which may result from greater colostral absorption, indicated by increased serum gamma-glutamyl trasferase. No difference was observed between genetic groups for average fecal score, however the F1 calves required fewer treatments with antibiotics for diarrhea. We conclude that crossing Holstein cows with Jersey sires reduces dystocia due to the ix smaller size of F1 calves at birth. The performance of crossbred calves is similar to the Holstein, from birth to 84 days of age, with higher immune status and requiring fewer treatments for diarrhea / A raça Holandesa predomina nos rebanhos leiteiros do Sul do Brasil, sendo conhecida pela elevada produção de leite com baixa concentração de sólidos, reduzida fertilidade e longevidade e elevada proporção de partos distócicos. O cruzamento com outras raças leiteiras especializadas, especialmente a raça Jersey, vem sendo empregado como uma opção para reduzir as deficiências da raça Holandesa. O objetivo deste trabalho foi avaliar a facilidade de parto de vacas da raça Holandesa inseminadas com Holandês ou Jersey e o desempenho dos bezerros oriundos destes acasalamentos quanto ao desenvolvimento, status imunológico e prevalência de diarréias nos primeiros dias de vida. O estudo foi desenvolvido no Centro de Ciências Agroveterinárias da Universidade do Estado de Santa Catarina (UDESC), em Lages SC. Utilizaram-se 40 vacas e novilhas inseminando-as aleatoriamente com Holandês ou Jersey, das quais, obtiveram-se 23 bezerros Holandês (11 machos e 12 fêmeas) e 17 bezerros mestiços (7 machos e 10 fêmeas). Os partos foram observados e uma escala para facilidade de parto entre 1 (fácil, sem auxílio) e 5 (extrema dificuldade) foi adotada. Após o nascimento, os bezerros foram alojados em bezerreiro com baias individuais e avaliados quanto ao peso, altura à cernelha, diâmetro torácico e diâmetro e comprimento de cabeça, sendo estas medidas repedidas semanalmente. Até uma hora após o nascimento, os bezerros receberam 2 litros de colostro e uma segunda dose até 8 horas após. Nos 2 dias seguintes, recebiam 4 litros/dia de leite de transição e a partir do 4º dia passavam a recebem 4 litros/dia de leite integral e alimento concentrado a vontade. No 42º dia os bezerros eram desaleitados e a dieta passava a ser o concentrado inicial adicionado de 20% de feno. Diariamente a oferta e a sobra de concentrado foram pesadas e o escore fecal avaliado em uma escala de 1 (fezes normais) a 4 (fezes líquidas). As coletas de soro sanguíneo procederam-se logo após o nascimento, com 24h, 15, 30, 42, 49 e 84 dias de idade, para avaliar a imunidade dos bezerros. Partos distócicos foram observados somente em bezerros da raça Holandesa (17,39%). Os bezerros F1 Holandês x Jersey apresentaram menor peso e altura ao nascer (35,2 Kg e 72 cm) em comparação aos Holandês (42,8 Kg e 76,3 cm), ao desaleitamento e no final do experimento (84 dias de idade), sem diferença em ganho de peso e crescimento em altura (P>0,05). Também não houve diferença entre os grupamentos genéticos para consumo de concentrado e conversão alimentar. Os bezerros F1 apresentam níveis mais elevados de proteínas totais e imunoglobulinas no soro sanguíneo com 24h e 15 dias de idade, o que pode ser vii resultado de maior absorção colostral, indicado por maior concentração sérica de gama-glutamil trasferase. Não foi observada diferença entre os grupamentos genéticos para escore fecal médio, entretanto os bezerros F1 necessitaram menos tratamentos com antibióticos para diarréia. Conclui-se que o cruzamento entre Holandês e Jersey reduz a distocia em razão ao menor tamanho dos bezerros F1 ao nascimento. Os bezerros mestiços comportam-se de forma semelhante aos da raça Holandesa em relação ao desempenho do nascimento até os 84 dias de idade, apresentando status imunitário mais elevado e necessitando menos tratamentos para casos de diarréia