Effects of protected protein supplementation on feeding, faecal nitrogen and reproduction in dairy cows

Context Protein is an essential nutrient in the diet of dairy cows, comprising rumen degradable protein and rumen undegradable protein (RUP). Balancing these fractions optimises nitrogen use, reduces waste and improves efficiency. Excess rumen degradable protein can harm reproduction by increasing urea and ammonia levels. Soybean meal, a key protein source, can be processed via heating or chemical methods to increase RUP. Aims This study evaluated the effects of two protein supplementation methods – protection with a binding agent and heat treatment – on feeding behaviour, nitrogen excretion and reproductive performance in early lactation dairy cows. Methods Cows (n = 36) at 38 ± 2.9 days in milk were assigned to one of three dietary treatments: a control group, receiving a total mixed ration with 16.42% CP and 5.15% RUP; a binder-protected group, with 66.9% of soybean meal treated with a binding agent (17.01% CP, 7.72% RUP); and a heat-treated group, where 66.9% of soybean meal was replaced with toasted soybean meal (16.12% CP, 7.73% RUP). Diets were fed for 42 days, following a 7-day adaptation period. Faecal nitrogen was measured weekly, and milk samples were collected to analyse composition (protein, fat and total solids). Nitrogen use efficiency was also calculated. Daily, dry matter intake, feeding visits, feed efficiency and milk yield were monitored. Fixed-time artificial insemination, preceded by an ovulation synchronisation protocol, was performed at 60 days in milk; pregnancy diagnosis was conducted 28 days later. Conception rates and number of inseminations were recorded up to 150 days in milk. Key results Cows in the binder-protected group group showed lower dry matter intake, greater feed and nitrogen use efficiency, and higher milk protein and fat contents. The binder-protected group and heat-treated group groups showed higher conception rates. Conclusions Binder-protected soybean meal enhances feed efficiency, reduces nitrogen excretion and improves reproductive outcomes, whereas heat-treated soybean meal also contributes to improved reproductive performance. Implications Incorporating binder-protected soybean meal can enhance feed efficiency, lower nitrogen waste and support better reproductive outcomes, aligning with goals for sustainable and profitable dairy production.