Short and mid-term effects on performance, health and qualitative behavioural assessment in Romane lambs in different milk feeding conditions

The common practise of artificially rearing some lambs from prolific meat breeds of sheep constitutes a welfare issue due to increased mortality rates and negative health issues. In this multidisciplinary study, we investigated the possible short and mid-term advantages of artificially feeding fresh ewe’s milk instead of commercial milk replacer on lambs’ growth, health and welfare. Romane lambs were either separated from their mothers on D3 and fed with Lacaune ewes’ milk (LAC, n=13) or milk replacer (REP, N=15), or they were reared by their mothers (MOT, n=15). On D45, they were weaned, gathered in single sex groups until the end of the study on D150. Lamb performance and biomarkers of overall health were assessed by measuring: growth, dirtiness of the perianal area, enteric pathogens in the faeces, total antioxidant status and redox status assessed by plasma reduced (GSH)/oxidized (GSSG) glutathione ratio, and immune response after vaccination against chlamydiosis. As an exploratory approach, blood cell transcriptomic profiles were also investigated. Last, Qualitative Behaviour Assessment was performed as an integrated welfare criteria. LAC and REP never differed in their average daily gain but grew less than MOT lambs in the early suckling period and just after weaning. No effect was detected afterwards. On D30, LAC and REP lambs had lower total antioxidant and higher redox status than MOT lambs but did not differ among themselves. LAC and MOT had a cleaner perianal area than REP lambs on D21, while faecal pathogen infection did not vary between the treatment groups. After vaccination, LAC also had a stronger immune response on D90 compared to REP lambs. Transcriptome analysis performed on D150 showed differential gene expression, mainly in relation to inflammatory, immune and cell cycle response, between male lambs of the LAC group and those of the MOT and REP groups. Based on Qualitative Behaviour Assessment, LAC lambs never differed from MOT lambs in their general activity and varied from REP only on D21; REP lambs were always more agitated than MOT lambs. In conclusion, artificial milk feeding impaired early growth rate, health, and emotional state mainly during the milk feeding period and at weaning. Feeding artificially reared lambs with fresh ewe's milk partly mitigated some of the negative effects induced by milk replacer but without achieving the full benefit of being reared by the mother. A flock of 32 ewes gave birth within a week under 24/24h supervision mainly to twins and triplets. On day 3 (D3), lambs were randomly allocated by sex and birth weight (minimum 2.5 kg) into 3 groups. In 2 of them, lambs were separated from their mother and artificially fed with either a milk replacer (REP group) or fresh ewes’ milk (lacaune milk, LAC group). In the third group, lambs remained with their dam (natural rearing, MOT group). Transcriptomic analyses were performed on 6 males and 4 females of the MOT group, 4 males and 7 females of the LAC group and 6 males and 5 females of the REP group. All animals were sampled at D150.