Changes in milk pH, milk protein, and udder development in late-pregnant ewe and effects on lamb serum total protein concentrations

Objective was to describe changes in milk pH, milk protein concentrations, and udder development in late-pregnant ewes. Ewes were synchronized, ram bred, and confirmed pregnant (n = 18) for potential cesarean section at 145 days of pregnancy (d 0). Udder score was assessed on days 22, 15, 10, 7, 4, 1, and 0 prepartum. Milk pH (digital pH meter) and protein concentrations (Brix refractometer) were monitored once daily from days 6 to 0 prepartum. Twelve ewes were selected for elective cesarean section and induced with 20 mg dexamethasone IM on day 1. At birth, lambs were assigned a vigor score (1 - 10) based on heart rate, respiratory rate, muscle tone, irritability reflex, and mucous membrane color. A total of 19 live and 3 dead lambs were delivered. Serum total protein (TP) was measured in lambs from 24 to 36 hours after birth. Statistical analyses were performed using R. Data on days prepartum and lamb TP were analyzed using ANOVA. Pearson’s correlation analysis was used to determine associations. There was moderate correlation in days prepartum with both udder development (r = 0.53, p < 0.001) and milk pH (r = 0.46; p < 0.001), but no correlation with milk protein concentrations (r = 0.11, p = 0.25). Days prepartum did not differ between udder scores of 0 (no development: 14 ± 3.8 days) and 1 (minor development: 12 ± 1.2 days; p = 0.96), but did change for scores of 2 (moderate development: 6.6 ± 0.5 days) and 3 (full development: 3.4±0.4 days; p ≤ 0 .03). Days prepartum differed when milk pH measured > 6.5 (4.4 ± 0.3 days), 6 - 6.5 (2.1 ± 0.2 days), and < 6 (0 ± 0 days; p < 0.001). Lamb TP was not affected by milk protein concentrations at d 0 (p = 0.96), but tended to be affected by vigor score (p < 0.06). We concluded that udder score and milk pH may be useful for predicting parturition in ewes. Additionally, assessing neonate vigor at birth can help influence colostrum management decisions.

Keywords: Milk pH, milk protein, neonate vigor, parturition, udder development

This manuscript was originally published in the journal Clinical Theriogenology Vol 12(3) Sept 2020.  Clinical Theriogenology is the official journal of the Society for Theriogenology (SFT) and the American College of Theriogenologists (ACT).  This content has been reproduced on the IVIS website with the explicit permission of the SFT/ACT.