Effects of dietary fat on fertility of dairy cattle: A meta-analysis and meta-regression

Abstract

Evidence is increasing of positive effects of feeding fats during transition on fertility and the adaptation to lactation. This study used meta-analytic methods to explore the effects of including fats in the transition diet on the risk of pregnancy to service (proportion pregnant) and calving to pregnancy interval. Meta-analysis was used to integrate smaller studies and increase the statistical power over that of any single study and explore new hypotheses. We explored the effect of fats and diet composition on fertility using meta-regression methods. Relatively few highly controlled studies are available providing detailed descriptions of the diets used that examined interactions between fat nutrition and reproductive outcomes. Only 17 studies containing 26 comparisons were suitable for inclusion in statistical evaluations. Reproductive variables evaluated were risk of pregnancy (proportion pregnant), primarily to first service, and calving to pregnancy interval. Production variables examined were milk yield, milk composition, and body weight. The sources of heterogeneity in these studies were also explored. A 27% overall increase in pregnancy to service was observed (relative risk=1.27; 95% confidence interval Knapp Hartung 1.09 to 1.45), and results were relatively consistent (I(2)=19.9%). A strong indication of a reduction in calving to pregnancy interval was also identified, which was consistent across studies (I(2)=0.0%), supporting a conclusion that, overall, the inclusion of fats does improve fertility. Further exploration of the factors contributing to proportion pregnant using bivariate meta-regression identified variables that reflected changes in diet composition or animal response resulting from inclusion of the fat interventions in the experimental diets fed. Increased fermentable neutral detergent fiber and soluble fiber intakes increased the proportion pregnant, whereas increased milk yield of the treatment group decreased this measure. Unexpectedly, the estimated energy costs of urea production also had a positive association with proportion pregnant. The limited number of suitable studies for the analysis highlights the need for more work to improve understanding of the critical nutritional factors affecting fertility. These factors include specific fatty acids in dietary interventions that contribute to increasing fertility of cows in dairy production systems.

Impacts of Macronutrients on Gene Expression: Recent Evidence to Understand Productive and Reproductive Performance of Livestock

“…Nutritional factors may have an influence on different stages of the reproduction starting form follicular growth to the birth of an offspring. Metaanalyses and meta-regression of nutritional effects on reproductive parameters demonstrated that there was a negative effect of soluble proteins and positive effects of lipids on reproductive performance in lactating dairy cows (Rodney et al, 2015). Although low heritability of reproductive traits indicating the complex and multifactorial nature of this trait, recent studies showed that the estimated genetic merit for reproductive traits is increasing (Berry et al, 2014).…”

Supplementation of dairy cows with docosahexaenoic acid did not affect ovarian activity

“…However, meta-regression of the difference in diets between treatment and control groups did not identify the reasons for these improvements in regard to the FA composition of the diet. The limited number of papers found and the positive results of this study support the need for further tasks exploring the effects of fat supplementation of the diet of the transition cow on fertility and the development of guidelines to assist study design in this field of research (Rodney et al 2015).…”

“…In a recent meta-analysis (Rodney et al 2015), authors concluded that feeding fats had a positive effect on fertility and had a tendency to increase production when given during the transition period. However, meta-regression of the difference in diets between treatment and control groups did not identify the reasons for these improvements in regard to the FA composition of the diet.…”

Relationship Between Dietary Fatty Acids and Reproductive Functions in Dairy Cattle

“…The fatty acid profile of the dietary fat may influence the propensity of animals to increase plasma progesterone (Dipak et al, 2013;Rodney et al, 2015). Mature ewes were infused intravenously with saline, soybean oil, or olive oil for 5h on d 9 through 13 of an estrous cycle .…”

“…The positive effects of dietary fat on fertility in dairy cows could be due to effects of certain dietary fatty acids on the pituitary, ovaries and uterus, rather than via improved energy status (Dipak et al, 2013;Rodney et al, 2015). It is believed that only certain dietary fats can suppress PGF2α production because specific fatty acids (polyunsaturated fatty acids; PUFA) are known to play a key role in PGF2α syntheses.…”