Effects of subacute ruminal acidosis on dry matter intake, rumen fermentation, blood variables, and conception rate in Holstein heifers

The objective of this study was to determine if experimentally induced subacute ruminal acidosis (SARA) reduces conception rates of Holstein heifers. One hundred and ten heifers were synchronized for artificial insemination by two injections of PGF2α in a 13-d interval and assigned randomly to two treatments. The control heifers received a diet containing 32% (DM basis) barley-based concentrate, while the SARA challenge group received a diet containing 68% of this concentrate started 3 d after the 2nd PGF2α injection and continued for seven days. Fortyone heifers from the SARA group and 39 heifers from the control group showed visible signs of heat and were inseminated. Heifers in SARA group had higher dry matter intake (DMI, 10.4 vs. 9.0 kg d^-1, P < 0.01) and lower rumen pH (6.02 vs. 6.45, P < 0.01) and fecal pH (6.71 vs. 6.97, P < 0.01). The SARA challenge increased rumen concentrations of lipopolysaccharide, lactate, propionate and valerate, but did not affect the concentrations of acetate, and butyrate. The challenge did not affect glucose, urea nitrogen, aspartate aminotransferase, calcium and cortisol concentrations in blood, but it lowered blood betahydroxy butyrate (P < 0.01). Induction of SARA markedly reduced first service conception rate tested by ultrasonography 28 d after insemination (53.7 vs. 71.8 %, P < 0.05). Additionally, 100% of control heifers that were confirmed as pregnant in the 28-d test were also pregnant at 60-d test, whereas this ratio was only 73.9% (P < 0.01) in SARA-challenged heifers suggesting that SARA had a persistent effect on reproduction. Results suggest negative effects of SARA on fertility of dairy heifers. 

Key words: metabolic acidosis, Fertility, Heifers, Conception rate.

Published in the proceedings of the Animal Nutrition Conference of Canada 2020. For information on the event, past and future editions, check out https://animalnutritionconference.ca/.