tissue mobilization to meet the nutritional requirements of a growing gravid uterus and strategies to mitigate its intensity in dairy cows

The study investigated the effects of different diets on late-pregnant holstein cows. twenty-one multiparous cows were grouped into three dietary treatments: a control diet, a diet with rumen-protected amino acids (methionine and lysine; paa), and a high-crude protein (high-cp) diet contained with plant source proteins. the cows were transferred to individual stalls 28 days before calving and remained until parturition. weekly measurements included the body weight (bw), body condition score (bcs), and back fat and eye muscle depths. blood and urine samples were taken for analysis of β-hydroxy butyrate (βhb), non-esterified fatty acid (nefa), cholesterol, and nitrogenous compounds. colostrum and placental attributes were collected at calving. results showed a 25% decrease in dry matter intake near calving, with stable bw and bcs. the cows that fed on high-cp, had the highest back fat and eye muscle depth. blood metabolite analysis revealed decreasing anabolic markers [albumin, plasma urea nitrogen (pun), cholesterol] and increasing catabolic markers (creatinine, βhb, nefa) toward calving. plasma 3-methylhistidine (3-mh) levels rose, indicating muscle mobilization. urinary excretion of allantoin, total urea nitrogen, and uric acid decreased significantly (p<0.001), reflecting increased nitrogen demand. the cows that fed with high-cp exhibited higher fecal nitrogen excretion, while the cows on paa had lower metabolic fecal nitrogen (mfn) levels. the calf bw was highest in the paa group, and their colostrum showed higher protein content and lower freezing points. this study highlights dynamic metabolic shifts in dairy cows during late pregnancy, with significant muscle and fat mobilization despite stable body metrics. high dietary cp could not prevent muscle mobilization, suggesting the need for adaptive feeding strategies. the results underline the importance of dietary supplementation, particularly paa, to meet the heightened nutritional demands during this critical period.