161 DIETARY ENERGY SOURCE IN PRIMIPAROUS DAIRY COWS DURING THE TRANSITION PERIOD: BLOOD METABOLITES AND FOLLICULAR CLASSIFICATION

Abstract

Solving reproductive problems of postpartum dairy cows has become one of the main targets of the scientific community even though the advances in this field are partial in most of the conducted research. There is a need to approach the problem with a multidisciplinary strategy that simultaneously includes nutritional and reproductive issues. Increasing the availability of glucogenic and lipogenic nutrients during the transition period has been hypothesised to improve energy balance and to decrease the incidence and severity of metabolic and reproductive disorders in early lactation. Based on the considerations mentioned above, the objective of this study was to compare the effects of a glucogenic or a lipogenic diet on blood metabolites and follicular dynamics in primiparous dairy cows during the transition period. Forty primiparous dairy cows received a lipogenic or glucogenic supplement during the transition period and were randomly assigned to 1 of 4 treatments [control; calcium salts of soybean fatty acids (CaS), Megalac-E; toasted soybean; and propylene glycol]. Diets were isocaloric and isoproteic. Blood samples were taken from each animal 10 and 5 days before the expected calving date and at days 7, 14, 21, 28, 35, and 42 postpartum. Ultrasound scanning was performed in all cows on Monday, Wednesday, and Friday up to day 45 postpartum. Follicles registered during ultrasound examination were classified in 4 categories: class I (3–5 mm), class II (6–9 mm), class III (10–15 mm), and class IV (>15 mm). Data analysis was performed using PROC GLM (SAS, 6.12, SAS Institute Inc., Cary, NC, USA, 1995). Metabolites and ovarian activity were analysed using a split-plot design. Pairwise comparisons of individual means were carried out using the Scott Knott and Duncan test. Values of P < 0.05 were considered statistically significant. Insulin and glucose concentrations were higher in the CaS group when compared with other treatments (P < 0.05). The lowest insulin and glucose concentrations were observed on cows supplemented with propylene glycol. Nonesterified fatty acid concentrations (NEFA) were lower for all treatments compared with the control group (P < 0.05). The most efficient follicular growth pattern during the postpartum period was observed in the CaS group, which was characterised by a reduction in the number of class I and II follicles and an increase in class III and IV throughout the trial. In general, smaller follicles go through recruitment and selection processes to bigger follicles and these follicles probably remain stable due to the fact that this particular follicular class represents a transitory phase in which there are always follicles going under the processes of selection and dominance. Overall, results suggest that calcium salts of soybean fatty acids reduced the dramatic metabolic and endocrine changes of primiparous dairy cows during transition period, which could be associated with better reproductive performance.