Influence of dietary energy on follicular development, serum gonadotropins, and first postpartum ovulation in suckled beef cows1

Abstract

Twenty-eight Hereford x Angus cows (4 yr of age) were used to determine the effects of pre- and postpartum dietary energy on performance and reproductive function in suckled beef cows. The experiment was designed as a 2 x 2 factorial with cows receiving either 70 (L) or 150% (H) of NRC recommended level of dietary energy before and(or) after parturition, resulting in four treatment combinations (L-L, L-H, H-L, H-H). Prepartum diets were fed for approximately 110 d, and postpartum diets were fed until either 10 d after the second postpartum ovulation or 150 d postpartum for those cows that failed to ovulate. Cows receiving low compared with high levels of energy before calving lost more (P less than .01) weight, body condition, subcutaneous fat, and longissimus muscle area before parturition and had calves with lighter (P less than .01) birth weights. Cows receiving low compared with high levels of energy postpartum lost more (P less than .01) weight, body condition, and longissimus muscle area after parturition. Low levels of energy before and after parturition decreased (P less than .01) milk production and calf weight at 70 d of age. Rates of cervical and uterine involution were unaffected by dietary energy treatments. Cows receiving high levels of energy prepartum had increased (P less than .01) mean concentrations and pulse frequency of LH in serum after parturition, and cows receiving high levels of energy postpartum had increased (P less than .05) pulse frequency of LH. Low levels of energy postpartum decreased (P less than .01) appearance rate of small (5.0 to 7.9 mm) and large (greater than or equal to 10 mm) follicles, and low levels of energy prepartum decreased (P less than .02) appearance rate of large follicles based on transrectal ultrasonography. Cows receiving high levels of energy prepartum had shorter (P less than .02) intervals from parturition to ovulation, and a higher (P less than .01) percentage of the cows that received high levels of energy postpartum ovulated by 150 d postpartum. In summary, prepartum level of dietary energy influenced birth weight and weight gain of calves, milk production, concentrations and pulse frequency of LH in serum, appearance rate of large follicles, and the interval to first ovulation. Postpartum level of dietary energy influenced milk production, weight gain of calves, pulse frequency of LH, appearance rate of small and large follicles, and the percentage of cows that ovulated after parturition.

Modelo de simulação do desempenho reprodutivo de fêmeas bovinas de corte com base no escore de condição corporal

“…Existem autores que destacam a importância das flutuações no ECC pós-parto (Ciccioli et al, 2003;Lalman et al, 1997;Perry et al, 1991;Vizcarra et al, 1998) e na ingestão de energia pré e/ou pós-parto (Wiltbank et al, 1962) no desempenho reprodutivo. No entanto, Lalman et al (1997) ressaltaram que, quando vacas primíparas passam por balanço energético negativo no período pré-parto, o ECCPAR passa a ser o fator mais importante na determinação da duração do período de anestro pós-parto.…”

Influence of Follicular Growth Stimulation on Fertility of Beef Cows Treated with eCG or FSH in FTAI Protocols

“…O bom índice de prenhez alcançado no grupo Controle deveu-se provavelmente à oferta, à qualidade de pasto e ao bom índice pluviométrico na região durante o período de realização do experimento. Este fato também confirma observações anteriores de que vacas em boa condição corporal e ganhando peso não necessitam suplementação com hormônios folículo estimulantes para atingirem taxas de prenhez em torno de 50% [10,16,17].…”

“…As relações entre o tamanho do FO, formação do corpo lúteo, a produção de progesterona e o desenvolvimento embrionário inicial estão associadas ao estabelecimento da prenhez em novilhas e vacas de corte [2,11,19]. Diversos estudos relacionam o menor diâmetro do FO em vacas de corte sincronizadas para a IATF com a baixa condição nutricional, com a amamentação e com o intervalo parto-tratamento [4,5,10,11,13].…”

Efeitos de carga animal, pastagem melhorada e da idade de desmame no comportamento reprodutivo de vacas primíparas

“…Existe vasta literatura indicando que o consumo reduzido de energia, no pré e pós-parto, retarda o crescimento dos folículos ovarianos após o parto, reduz o tamanho dos folículos dominantes, diminui o número de folículos secretores de estrógeno e aumenta a persistência dos folículos menores subordinados, influenciando negativamente o intervalo do parto à primeira ovulação (Wiltbank et al, 1962;Randel, 1990;Perry et al, 1991;Spitzer et al, 1995).…”