Original title: Effects of commercial direct-fed microbials and zinc-methionine supplements on growth performance in preweaning Holstein calves under commercial rearing conditions
Ahmadreza Alipour, Mahdi Ganjkhanlou, Abolfazl Zali, Mahdi Dehghan-Banadaki +2 · August 2026
Farmers want young calves to grow well before they stop drinking milk. Scientists tested if adding beneficial live microbes, called direct-fed microbials, or a zinc and amino acid mix called zinc-methionine helps them develop. Microbes support gut health and digestion, while zinc helps cells grow, and both nutrients help calves eat more dry food. Researchers tested these additives on seventy-two newborn calves. Both supplements worked well on their own. Calves given the live microbes grew faster every day, gained more body weight, and grew taller at the shoulders. Calves given zinc-methionine also ate more dry feed, gained more body weight, grew wider hips, and grew taller. The beneficial microbes raised blood sugars, proteins, and cholesterol, while zinc raised the blood protein albumin. However, feeding both supplements together gave no steady extra boost compared to giving them by themselves.
You are baking cookies and decide to add chocolate chips. They make the cookies better. Then you also add nuts, expecting even better cookies. But the cookies with both are not necessarily better than with just chocolate chips. In this paper, the two feed additives are like those ingredients; each helps calf growth, but the combination doesn't outperform the single ones.
Dairy farmers want calves to grow faster and healthier before weaning. This study shows that adding direct-fed microbials or zinc-methionine to calf feed can increase weight gain, feed intake, and body measurements. However, using both together didn't give extra benefits, so farmers might choose one additive based on cost or availability.
The study was conducted under commercial rearing conditions but with a limited number of calves (72) from a single location. It does not establish long-term effects beyond preweaning or mechanisms of action. The lack of synergistic effect may depend on the specific doses used.
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Effects of commercial direct-fed microbials and zinc-methionine supplements on growth performance in preweaning Holstein calves under commercial rearing conditions — Ahmadreza Alipour, Mahdi Ganjkhanlou, Abolfazl Zali et al. — Veterinary and animal science — doi:10.1016/j.vas.2026.100845
Abstract licence: CC BY
Explanation generated by Synthesis from the abstract — it is not the original paper.