PSI-19 - Functional rumen microbiological characteristics of conventionally versus artificially reared triplet Polypay lambs from birth to weaning

Abstract: Artificial rearing remains an integral practice in sheep production largely due to the unique prolificacy of ewes as opposed to other species. Research has demonstrated slower growth and reduced performance of lambs reared on milk replacer when compared to conventionally reared lambs, but little is known about the functional development of the rumen microbial community. The objective of this study was to evaluate differences in functional rumen microbiological characteristics between conventionally (CR) and artificially (AR) reared lambs. We hypothesized that AR lambs would have slower rumen microbial community development than CR lambs, with consequent impacts on circulating metabolites. Nine Polypay ewes bearing triplets were selected for the study. One lamb from each set was removed from the ewe 24 hours after birth and placed on milk replacer. AR lambs were weaned on day 45 and CR lambs were weaned on day 60. A standard concentrate creep diet and alfalfa hay was made available ad libitum to both CR and AR lambs throughout the entire pre-weaning period. Rumen samples were collected via oral intubation and blood samples via jugular venipuncture on days 2 (blood only), 15, 45, and 60. Rumen bacterial functional guilds were enumerated via serial dilution and serum metabolites quantified via LC-MS. Data were analyzed using PROC MIXED in SAS (v. 9.4, SAS Inst. Inc., Cary, NC). No differences between treatments were found for average daily gain (g d^-1) over the pre-weaning period (P = 0.12). Cellulolytic bacteria in the rumen increased during the pre-weaning period (P < 0.01), with proliferation noted for both treatments from day 15 to day 45 (P < 0.05). However, the magnitude of this proliferation differed between pre-weaning management, with a 1,000-fold increase for CR lambs, but only a 10-fold increase for AR lambs from day 15 to day 45 (P < 0.05). This resulted in a 100-fold difference between treatments on day 45 which persisted to day 60 (P < 0.05). Circulating β-hydroxybutyrate concentrations also increased over the pre-weaning period (P < 0.01), and were consistently lower for AR (134.17 ± 15.04 mmol L^-1) than CR lambs (209.21 ± 15.04 mmol L^-1 ; P = 0.01). Conversely, circulating glucose decreased in both AR and CR lambs from day 2 to 60 (P = 0.06), with CR lambs having lower concentrations detected on days 2 and 45 (P < 0.05). These results indicate potential delays in rumen development of AR lambs, supported by the differences observed in rumen cellulolytics and circulating metabolites when compared to CR lambs. These results could suggest implications for impaired dietary utilization and subsequent growth of AR lambs post-weaning, especially those managed on high-forage diets.