Associations among Mammary Ultrasound Measurements, Milk Yield of Non-Dairy Ewe Lambs and the Growth of Their Single Lambs

Abstract

Mammary cistern size was positively correlated with milk yield of mature dairy ewes, but the association in ewe lambs is unknown. This experiment aimed to examine the associations between mammary ultrasound measurements and the milk yield of ewe lambs at one year of age and to determine the accuracy of using maternal mammary ultrasound to predict single lamb growth rates. Single-bearing ewe lambs (n = 45) were randomly selected and 30 were milked once at weeks three (W3), five (W5), and seven (W7) of lactation. Mammary ultrasound scans were performed at day 110 of pregnancy, W3, W5, W7, and weaning (L69). Single lambs (n = 30) were weighed at birth and at each mammary scanning event. Udder measurements explained 26.8%, 21.4%, and 38.4% of the variation in milk yield at W3, W5 and W7, respectively, and 63.5% and 36.4% of the variation in single lamb growth to W3 and to L69. This ultrasound technique was more accurate in predicting single lamb growth to W3 than milk yield and may enable the identification of pregnant ewe lambs whose progeny would have greater growth rates. More research is needed to identify accurate indicators of superior milk yield and determine whether ultrasound could be used to select ewe lambs.

Effects of Increased Growth Rates Prior to the First Breeding as Ewe Lambs and Pregnancy Rank on Mammary Glands of Two-Year-Old Ewes

“…The variation in lamb growth rate explained by ewe udder measures was moderate and greater from birth to weaning (53%) than birth to early lactation (22%). The variation explained in lamb growth rate to weaning was greater than that reported in Haslin et al [14] and [15] in ewe lambs, but still only explained half of the variation in lamb growth to weaning. The differences with the findings in Haslin et al [15] may be due to the age of the lambs when weaning measures were recorded.…”

“…Moreover, the predicted lamb growth rates included twin lambs, which are known to have slower growth rates than single lambs [31]. Predictions of lamb growth using ultrasound measures, therefore, may differ between single and twin lambs and may explain the differences with Haslin et al [14] and [15], which included only single lambs. The differences observed could also be due to the age of the ewes.…”

“…The differences observed could also be due to the age of the ewes. In Haslin et al [14,15], ultrasound examinations were performed on ewe lambs. Ewes have been reported to produce less milk during their first than second lactation [10,43], which may also result in differences as ewes age.…”

“…Mammary gland cistern size during lactation is positively associated with milk production of both dairy [11,12] and non-dairy ewes [13]. In Haslin et al [14], the depth of the mammary gland cistern in pregnancy and week three of lactation was positively correlated with milk yield in the third week of lactation of ewe lambs rearing single lambs. In Haslin et al [15], single-lamb growth to weaning was positively associated with parenchymal depth in pregnancy and gland cistern size in early lactation.…”

“…In Haslin et al [15], single-lamb growth to weaning was positively associated with parenchymal depth in pregnancy and gland cistern size in early lactation. Meanwhile, growth to weaning of single lambs was negatively associated with mammary fat pad depth in the seventh week of lactation and positively associated with depth of the fat pad at weaning [14]. Currently, no data have been published on the associations between mammary gland ultrasound measures of older non-dairy ewes and the growth of their lambs.…”