Effects of galacto-oligosaccharides and microbiota transfer on lung health and performance of calves

Bovine respiratory disease is a major multifactorial health issue in calves. Our objective was to evaluate the effects of galacto-oligosaccharide supplementation, microbiota transfer, and their interaction on lung health and performance of calves. A total of 180 male Holstein-Friesian calves at 18 ± 3.6 d of age received 1 of 4 treatments according to a 2 × 2 factorial design for 8.5 wk (period 1). Calves received galacto-oligosaccharides (GOS) via the milk replacer or not (CON) and received a microbiota transfer (MT) or not (MOCK). The MT strategy consisted of a combination of an oral rumen microbiota transfer and a fecal microbiota transfer supplied orally and rectally. The MT or MOCK procedure was applied 3 times in the first week after arrival and was repeated within a week after a group antimicrobial treatment. Clinical health was scored weekly, and BW was measured every 4 wk. Bronchoalveolar lavage fluid (BALF) and blood samples were collected biweekly from a subset of calves (n = 108). After period 1, all calves received the same control milk replacer for 4 wk (period 2), during which performance and clinical health were measured. Clinical scores increased from wk 1 to 3, and BALF IL-8 concentrations increased with time in period 1. This high infection pressure resulted in a requirement of 6 group antimicrobial treatments (supplied to all calves). Supplementation with GOS increased the ADG adjusted to equal solid feed intake (+27 g/d) in period 1 and tended to increase it (+45 g/d) in period 2. Supplementation with GOS decreased clinical scores in wk 1 and 3 (in the absence of MT) but tended to increase it in wk 6. Furthermore, GOS tended to decrease rectal temperature in period 2. Cytokine concentrations in BALF and blood were not affected by GOS, but the percentage of lymphocytes in BALF was increased by GOS, accompanied by a decrease in lymphocyte and an increase in neutrophil percentage in plasma. Microbiota transfer reduced plasma white blood cell concentration, related to a relative decrease in plasma neutrophils. Microbiota transfer reduced the percentage of BALF lymphocytes, and in wk 5, it also reduced the BALF concentration of TNFα. However, MT did not affect performance. At the start of period 2, MT even increased clinical scores in the absence of GOS, resulting in a higher individual antimicrobial treatment supply to MT calves in period 2, ultimately reducing the rectal temperature of MT calves at the end of period 2. Hardly any interactions between GOS and MT occurred, suggesting the absence of an additive relation. In conclusion, GOS improved performance and even tended to increase it after GOS supplementation ended, but this was not related to lung health. Microbiota transfer affected some inflammatory parameters, pointing toward reduced systemic and respiratory inflammation, but this was not reflected in clinical health, which even decreased in the carry-over period.