Effects of energy sources on milk production and reproduction of dairy cows

[摘要] ENGLISH ABSTRACT: Two main objectives were investigated in this study, conducted at the Elsenburg Research Farm of the Western Cape Department of Agriculture (WCDA). The first objective was to study the effect of nutritional treatments differing after calving in energy levels and sources on plasma metabolites and live weight (LW) changes, milk production and milk composition, ovarian follicular dynamics and oestrous activity, as well as fertility traits of dairy cows. The second objective was to investigate the effects of two late prepartum diets differing in non-fibre carbohydrates (NFC) and protein levels on milk production and milk composition, LW changes and fertility traits of dairy cows in the subsequent lactation. Three trials were conducted in this study. The first trial explored the effect of energy-dense ingredients like fat or starch on milk production and milk composition, plasma metabolites, LW change and fertility of lactating dairy cows. In this study, pregnant Holstein heifers and dry cows were similarly managed and fed prepartum. Following calving, they were allowed to graze ad libitum on kikuyu-ryegrass pasture, and received supplements that differed in terms of inclusion levels and types of concentrates. Holstein cows in the control group received 7 kg/day of a control concentrate supplement for both primiparous and multiparous groups, while treatments consisted of 11.6 and 12.6 kg/day for primiparous and multiparous cows, respectively. Supplements in treatments contained high starch-low fat (HSLF) and high starch-low fat/low starch-high fat (HSLF-LSHF) levels. The control and HSLF concentrates were offered from calving to 154 days in milk (DIM). The HSLF supplement was a glucogenic concentrate containing maize as the energy source. The HSLF-LSHF supplements were combinations of a glucogenic concentrate offered for the first 60 DIM as per treatment HSLF and followed from 61 to 154 DIM by a lipogenic concentrate containing wheat bran and calcium (Ca)-salts of long-chain fatty acids as the energy sources. The postpartum diets were formulated to be isonitrogenous. The control diet contained low energy level (2.47 Mcal ME/kg DM) and provided 457, 104 and 40 g/kg of NDF, starch and fat on DM basis, respectively. The HSLF diet contained high energy level (2.71 Mcal ME/kg DM) and offered 341, 242 and 35 g/kg of NDF, starch and fat on DM basis, respectively. The HSLF treatment was formulated to increase plasma insulin and glucose levels in order to reduce the magnitude of the NEB and encourage the early return of oestrous cyclicity after calving. In the HSLF-LSHF combination treatment, the high starch-based diet initially aimed to achieve the same objective of the HSLF treatment during the first 60 DIM. The LSHF diet contained high energy level (2.70 Mcal ME/kg DM) and provided 388, 137 and 58 g/kg of NDF, starch and fat on DM basis, respectively. Secondly, the LSHF diet was fed from 61 DIM to decrease plasma insulin and improve plasma cholesterol in order to increase the size of the ovulatory follicle as well as promote embryo development.The second experiment trial was simultaneously conducted with the first trial using the same feeding treatments. In this trial, the same objectives of the diets were evaluated for ovarian follicular dynamics and oestrous activity of multiparous cows after being synchronized by means of the Ovsynch protocol at 80 ± 10 DIM without artificial insemination (AI). Results on plasma metabolites showed that postpartum levels of non-esterified fatty acids (NEFA) and β-hydroxybutyrate (BHB) did not differ between nutritional treatments for multiparous cows, but levels increased (P < 0.05) for the control in comparison to HSLF and HSLF-LSHF treatments for primiparous animals. In addition, plasma urea levels were higher (P < 0.05) in both primiparous and multiparous animals receiving HSLF and HSLF-LSHF concentrates, compared to the control concentrate. The postpartum LW was the lowest (P < 0.05) and LW loss was greater (P < 0.05) in cows in the control in comparison to HSLF and HSLF-LSHF treatments in both primiparous and multiparous cows. Findings on productive responses showed that the milk yields and 4 % fat corrected milk (FCM) yields of both primiparous and multiparous cows in HSLF and HSLF-HFLS treatments were higher (P < 0.05), compared to cows in the control. In the primiparous group, the HSLF diet enhanced (P < 0.05) milk protein content whereas HSLF and HSLF-HFLS diets resulted in increased milk lactose content (P < 0.05). In multiparous group, HSLF treatment increased (P < 0.05) milk lactose content. Results of ovarian follicular dynamics and oestrous activity showed that dimensions of the ovaries and the preovulatory follicle as well as numbers of follicles within different classes in dairy cows were similar between nutritional treatments. However grazing cows receiving high (12.6 kg/day) levels of concentrates in the HSLF and HSLF-LSHF treatments recorded a higher number of total follicles (P < 0.05), compared to those on the low (7 kg/day) level of concentrate in the control group. Results of reproductive performance showed no nutritional effects in both primiparous and multiparous cows on the interval calving to first service, the percentage of cows serviced for the first time within the 80 DIM, pregnancy rate at first service, number of services per conception, interval days open and the pregnancy rate at 100 DIM.However, the conception rate at 150 DIM in both primiparous and multiparous groups improved (P < 0.05) in cows fed HSLF and HSLF-LSHF concentrates, in comparison to the control.The third trial was conducted to evaluate the effect of two late prepartum nutritional treatments on subsequent LW changes, milk production and milk composition, and fertility traits of Holstein dairy cows. Pregnant heifers and dry cows received a similar level and type of prepartum concentrate associated either unchopped oat hay ad libitum (control) or ad libitum intake of a partial total mixed ration (pTMR, treatment). The pTMR consisted of oat hay (48%), lucerne hay (43%) and soybean oil cake meal (9%). The prepartum treatment was designed to optimise rumen digestion and fermentation through improved prepartum intake of NFC and protein per kg on DM basis with an objective of reducing the extent of a periparturient negative energy balance (NEB) in comparison to the control. Following parturition, primiparous and multiparous cows received 7 kg/day of concentrate while grazing ad libitum on kikuyu-ryegrass pastures from calving to 120 DIM. Results showed that prepartum LW was similar for both primiparous and multiparous groups. In the primiparous group, the prepartum treatment significantly improved (P < 0.05) postpartum LW, with 20 kg more weight at LW nadir, compared to the control. However, no prepartum nutritional effects were detected on postpartum LW traits and LW loss for multiparous cows. Milk yields and milk composition were similar between the control and treatment for both primiparous and multiparous groups. Primiparous cows in the control group had a longer interval from calving to first service (P < 0.05), compared to those in treatment group. However, this improvement did not turn into increased conception rates of primiparous cows at 120 DIM. Similarly, prepartum diet effects in multiparous cows showed no postpartum differences in conception rates at 120 DIM.It can concluded that there is definite merit in the use of energy levels and sources for improving production responses, plasma metabolite profiles and LW change, ovarian follicular dynamics and fertility of grazing dairy cows. These improvements are related to nutrient composition and levels of total energy intake, controlling the profile of nutrients absorbed in the gastrointestinal tract (GIT) and their hepatic partitioning to various body tissues for metabolic requirements of dairy cows. This modulation has probably influenced the hypothalamic-pituitary-ovarian-uterine axis through improved nutritional status and optimized the energy carry-over effect into fertility success, while sustaining milk production. However, feeding fibre-based diets differing in NFC and protein levels in the late prepartum period showed no benefit in either milk production or conception rates of dairy cows in the subsequent lactation. The lack of significant differences of prepartum dietary effects on milk production and conception success can be related to the prepartum feeding period and the relatively low number of animals per treatment used in the study. Further investigations should be undertaken using different inclusion and types of energy sources in prepartum and postpartum dairy cows on metabolic and hormonal responses that can improve restoration body reserves and benefit chronological sequences of the reproductive process such as postpartum health, uterine regression, resumption of oestrous cycles, conception, and embryo/pregnancy survival until the next calving.

[发布机构] Stellenbosch University