Abstract
ABSTRACT - This study investigated the effect of a supplement containing whole rice bran and crude glycerin for 21 days before mating on metabolic, productive, and reproductive responses of 28 primiparous suckling beef cows. Cows were randomly assigned to a control group (CON, n = 14), grazing on grasslands, and a supplemented group (SUP, n = 14), grazing on grasslands and supplemented daily individually with 1 kg dry matter (DM) of whole rice bran + 550 mL crude glycerin (224 g kg−1 DM of methanol) per cow. After 33 days of natural mating, cows that had not expressed estrus were subjected to a fixed-time artificial insemination protocol. Ten days after the insemination program, bulls were reintroduced for 21 days. Supplementation increased milk yield (SUP: 5.7±0.2 vs. CON: 5.0±0.2 kg d−1), milk protein content (SUP: 3.1±0.2 vs. CON: 2.8±0.2%), and body weight of cow (SUP: 379±2 vs. CON: 373±2 kg) and calf (SUP: 150±2 vs. CON: 142±2 kg). Supplementation improved the energy balance, increased plasma concentrations of cholesterol (SUP: 223.2±6.4 vs. CON: 202.1±6.4 mg dL−1) and glucose (SUP: 72.0±1.2 vs. CON: 68.6±1.2 mg dL−1), and reduced non-esterified fatty acids (SUP: 0.45±0.02 vs. CON: 0.56±0.02 mmol L−1). The percentage of cows on superficial anestrous after supplementation was greater in SUP than in CON group (57 vs. 21%, respectively); however, no difference in final pregnancy rate was found (SUP: 79 vs. CON: 64%). There was no evidence that the ingestion of crude glycerin with high content of methanol induced clinical or hepatic disorders. Supplementation of whole rice bran and crude glycerin is not toxic, and can improve the energy balance, reflecting in increase in milk yield and calf growth, with a slight effect on the reproductive activity.
Highlights
In extensive pastoral systems for meat production, primiparous suckled cows have the lowest reproductive efficiency and wean the lightest calves, which reduces the productivity of the herd (Bellows et al, 1982)
The nutrient supply of grasslands during the winter is insufficient to meet the requirements of the growing fetus in the last third of the pregnancy period, causing a negative energy balance that continues during early postpartum due to the demand for milk production (Bell, 1995; Astessiano et al, 2013)
The nadir of body condition score (BCS) was reached in the 4th week postpartum and remained low until the beginning of the supplementation period
Summary
In extensive pastoral systems for meat production, primiparous suckled cows have the lowest reproductive efficiency and wean the lightest calves, which reduces the productivity of the herd (Bellows et al, 1982). The main cause of reproductive failure is the prolonged postpartum anestrus, induced by undernutrition (Short et al, 1990; Hess et al, 2005) and suckling (Williams, 1990). The nutrient supply of grasslands during the winter is insufficient to meet the requirements of the growing fetus in the last third of the pregnancy period, causing a negative energy balance that continues during early postpartum due to the demand for milk production (Bell, 1995; Astessiano et al, 2013). Short-term supplementations before or during the mating period, with or without association with temporary weaning, are alternatives to increase pregnancy rates in cows with sub-optimal BCS (Pérez-Clariget et al, 2007; Soca et al, 2013). The main disadvantage of crude glycerin is that its methanol content can impair liver function (Schröder and Südekum, 1999)
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