Letter to the Editor: Regarding the article “Comparison of milk replacer composition and effects on growth and health of preruminant lambs, and health-associated costs of artificial rearing,” by

Abstract

The April 2021 issue included an article by McCoard et al. (2021). This letter brings to the attention of readers several fundamental issues relating to the study design and the conclusions reported. The cost and scarcity of skim milk powders has driven research into alternative protein sources for young ruminants (Terosky et al., 1997; Lammers et al., 1998). Careful trial design, ensuring diets have a very comparable nutrient profile (Toullec et al., 1994) have improved our understanding of the suitability of different raw material sources for milk replacers (MR) for young animals. Research also has shown that the osmolality of MR, determined by the lactose and mineral contents of the MR (Amado et al., 2019; Wilms et al., 2020), will affect both rate of gastric emptying and DM content of feces produced by lambs. The authors conclusions that MR containing vegetable ingredients are not suitable for feeding to neonatal lambs in the first 5 to 6 wk of life and that increased systemic antibiotic use is a consequence of MR composition are not supported by the results presented. The conclusion that greater fecal moisture observed in lambs fed a milk replacer containing hydrolyzed wheat protein was a consequence of, or caused by, disease is not supported by the results presented and is more likely a consequence of the osmolality of the reconstituted MR, which is influenced by both the nutrient composition of the MR and the rate at which MR is mixed with water. A comparative assessment of the suitability of different ingredients for use in MR requires that the comparison be made using MR with an equivalent nutrient composition. Thus, it is not possible to conclude that MR containing vegetable (wheat in the case of this study) protein and fat sources is inferior and should be avoided.