73 Effect of Rate of Gain During Early Gestation on Colostrum and Milk Composition in Beef Heifers

We evaluated effects of rate of gain during the first 84 d of gestation on composition of colostrum and milk. At breeding, forty-five Angus-based heifers received either a basal total mixed ration allowing 0.28 kg/d gain [low gain (LG), n = 23] or basal diet plus starch-based supplement allowing 0.79 kg/d gain [moderate gain (MG), n = 22] for 84 days. Heifers were then managed on a common diet until parturition. Colostrum samples (50 mL) were collected before first suckling. Milk samples (50 mL) were collected 6 hours after calf removal on d 62 ± 10 and 103 ± 10 postpartum. Samples were collected by stripping each teat 15 to 20 times after discarding the first 5 strips. At d 103 sampling techniques were compared by collecting a second sample after 1 mL oxytocin administration and 90 sec lag. Data were analyzed using the GLM procedure of SAS. Fat, protein, somatic cell count (SCC), milk urea nitrogen, and other solids were analyzed in colostrum for effect of treatment, whereas milk was evaluated for effects of treatment, day and their interaction. Heifer was experimental unit and significance was set at P ≤ 0.05. Colostrum SCC was greater (P = 0.05) in LG (6,949 ± 739 cells/mL) than MG (4,776 ± 796 cells/mL). In milk, protein and other solids were greater (P ≤ 0.03) in MG (3.02 ± 0.03 and 6.20 ± 0.02 %, respectively) than LG (2.87 ± 0.03 and 6.14 ± 0.02 %, respectively). On d 103, oxytocin administration and extended lag time after teat stimulation (0.96 ± 0.05 %) increased fat content in milk (P < 0.01) compared with immediate milk sample collection (0.34 ± 0.05 %). Nutrition during early gestation had a sustained impact on milk composition and techniques of oxytocin administration results in greater milk fat content.

Factors affecting milk ejection and removal during milking and suckling of dairy cows

The release of oxytocin and milk ejection occurrence in response to teat stimulation are crucial for fast and complete milk removal during milking or suckling. The milk ejection reflex can be disturbed at central or peripheral level under different experimental and practical conditions. The central disturbance results in the lack or insufficient ejection of the alveolar milk into the cistern due to inhibited oxytocin release from pituitary into the blood circulation. The important role in the pathophysiological regulation of the inhibited release of oxytocin is played by an opioid system. Endogenous opioids have suppressive effects on oxytocin release under the normal conditions of milk removal. However under the conditions of disturbed milk ejection their role in dairy cows was not confirmed. Other possible mechanisms involved in the central inhibition of oxytocin release are discussed. In dairy cows as compared with rats the mechanisms involved in the regulation of oxytocin release at the central level remain unclear. The central inhibition of oxytocin release has often been observed in dairy practice during milking of primiparous cows after parturition, suckling by alien calf, calf removal before milking, milking of cows in the presence of own calf, relocation and milking in an unknown milking place. If sufficient released oxytocin cannot induce the transfer of milk from alveoli to cistern, peripheral mechanisms are involved. Peripheral mechanisms are related to the increased levels of catecholamines and/or activation sympathetic nervous system at the udder level. In conclusion, the release of oxytocin and milk ejection efficiency can be very easily suppressed by many factors. The effect of milking conditions on regulation of milk ejection has to be considered. Thus the physiological requirements of dairy cows have to be respected.

EFFECT OF TEMPORARY CALF REMOVAL NUMBERS IN TIMED ARTIFICIAL INSEMINATION PROTOCOLS ON WEANING WEIGHT FROM NELORE CALVES

Objetivou-se avaliar os efeitos causados pelo número de remoções temporárias de bezerros (RTB) Nelore durante o protocolo de inseminação artificial em tempo fixo (IATF) sobre o peso a desmama, além do efeito do mês de nascimento e da interação entre eles. Vacas (n = 271) com mais de 30 dias pós-parto foram sincronizadas com o seguinte protocolo de IATF: Dia 0: inserção de dispositivo intravaginal de progesterona + 2,0 mg de benzoato de estradiol; Dia 7: aplicação de 12,5 mg de dinoprost-trometamina; Dia 9: remoção do dispositivo de progesterona + 1,0 mg de cipionato de estradiol + RTB; Dia 11: IATF + retorno dos bezerros as vacas. Os bezerros cujas mães emprenharam após a primeira IATF foram submetidos a RTB apenas uma vez, já aquelas encontradas vazias após 30 dias foram ressincronizadas e seus bezerros foram submetidos a RTB pela segunda vez. O peso à desmama foi ajustado para 210 dias. A análise de estatística foi realizada pelo programa SAS. Não houve efeito do número de remoções temporárias no peso ao desmame (P > 0,05), porém, o mês de nascimento afetou esta variável (P <0,05). Concluiu-se que, o número de RTB em protocolos de IATF durante a estação de monta não afetou o peso à desmama dos bezerros. No entanto, o mês de nascimento afetou o peso à desmama de bezerros de corte, uma vez que aqueles que nasceram no início da estação de nascimento foram mais pesados.

Serum progesterone concentration and conception rate of beef cows supplemented with ground corn after a fixed-time artificial insemination protocol

The effects of different levels of finely ground corn (FC) supplementation to grazing beef cows after fixed-time AI (TAI) on serum progesterone (P4) concentrations on day 7 and conception rates on day 28 after TAI were investigated. Three hundred and sixty-four lactating multiparous Brangus cows had follicular and luteal activity synchronized by treatment with estradiol benzoate (Estrogin; 2.0mg IM) and insertion of intra-vaginal P4 releasing device (CIDR) on day -11, followed by treatment with PGF2α (Lutalyse; 25mg IM) on day -4, CIDR and calf removal on day -2, and treatment with GnRH (Fertagyl; 100µg IM) TAI and calf return on day 0. On day 0, cows were randomly allotted in one of the following FC supplement treatments: G1 - 2kg/day from day 0 to 21; G2 - 2kg/day from day 0 to 7, and 6kg/day from day 8 to 21; G3 -6kg/day from day 0 to 7, and 2kg/day from day 8 to 21; and G4 -6kg/day from day 0 to 21. Blood samples were collected on day 7, and pregnancy was determined by ultrasonography indicating the presence of a fetus on day 28. Cows supplemented with 2kg/d of FC had higher serum concentration of P4 on day 7 than cows supplemented with 6kg/d (1.58 vs. 1.28ng/mL; P<0.01; SEM = 0.08). Cows from G4 had higher conception rates compared to G1 cows (58.4 vs. 41.9%, respectively; P<0.05). The level of supplemental energy intake after TAI is negatively associated with following serum P4 concentrations, but positively associated with conception rates of grazing beef cows.