Positive consequences of maternal diet and post-natal rumen inoculation on rumen function and animal performance of Merino lambs

Neonatal modification of the microbial inoculum entering the gastrointestinal tract may alter the rumen microbiome and consequently alter pre- and post-weaning rumen fermentation and growth of lambs. This study aimed to determine (1) if modifying the rumen by providing ewes with lipids differing in rumen-availability in late gestation and lactation would affect performance of the lamb offspring and (2) whether cross-inoculation of neonatal lambs with digesta from sheep on an alternate diet would modify the fermentation, size, and characteristics of the developing rumen and performance of lambs. Two diets were offered ad libitum to 36 pregnant ewes (and to their lambs after lambing) from 1 month pre-lambing until 2 weeks after weaning, after which lambs were grazed in treatment groups in paddocks. Diets consisted of 92% of a blend of oaten and lucerne chopped hay, 4% molasses and 4% fat (coconut oil – CO or protected fat – PF). Newborn lambs were inoculated weekly while suckling (weeks one to eight postnatal) with fresh rumen fluid from donor ewes eating CO or PF diets, or were inoculated with water. Lamb body weight, condition score, wool growth, rumen fermentation, and rumen development were studied during the first 5 months of life of the lambs. Diet and inoculation affected dry matter intake after weaning (P < 0.05), being lower in lambs eating CO or inoculated with water. Feeding of CO instead of PF reduced the protozoa population and daily methane production of lambs (P < 0.05). Type of gut inoculum had an effect on the concentrations of acetate, propionate, butyrate, total volatile fatty acids, and total protozoa numbers in the rumen of lambs during lactation. By weaning, effects of post-natal inoculation were only apparent for the concentration of butyrate and the protozoal population. It is concluded that dietary fat can affect rumen development and fermentation of the lambs. In addition inoculation with exogenous rumen fluid can modulate some aspects of rumen fermentation. However, lamb performance evaluated at weaning and at 5 months after birth was not altered by either diet or early-life inoculum, suggesting that while the rumen microbiome may have plasticity in its composition, microbial changes do not necessarily result in improved animal performance.