The Use of Ultrasonography to Examine Mammary Gland Development in Ewe Lambs with Different Live-Weight Gain Profiles between 12 and 20 Weeks of Age.

This study aimed to non-invasively examine mammary composition of lambs on differing feeding levels, between weaning and puberty (70-260 days-of-age).

Feeding during critical periods between birth and puberty appears to affect mammary growth. Current knowledge suggests that high growth rates and in particular, fat deposition in the udder before puberty, can have a negative influence on mammary growth and future milk production It has been hypothesised that this negative effect on milk production is due to the reduction in age at puberty and first pregnancy achieved through faster growth, and the associated immaturity of the mammary tissue. However, the size of the fat pad also dictates the maximal area into which the mammary parenchyma can grow and hence may determine the gland’s ultimate production potential. Thus early simple measurement of mammary tissue using ultrasound may provide a means to select animals with higher milking potential prior to (a) puberty and/or (b) insemination and first milking.

East-Friesian cross ewe lambs at 70 days-of-age were randomly allocated to two levels of pasture feeding (High nutrition plane consuming on average 1.34 kg DM/head/day and a 70% nutrition plane consuming on average 0.85 kg DM/head/d) until 140 days (n=60/group). At day 140 lambs were reallocated to nutrition treatment using a crossover design resulting in four treatment groups (n=30/group). After the end of the treatment period (d260), mammary gland size was imaged using ultrasonography. Total depth of the mammary gland, putative fat pad and parenchyma, at the widest point for each sub-compartment (estimated from 4 images/animal), was used as a proxy for tissue volume. The ratios of the different tissue depths were calculated. Data were analysed using a linear mixed model with Image, 70-140d Treatment and 140-260d Treatment as fixed effects, animal as random effect and live weight as a covariate.

Lamb liveweights at day 260 were 36.2, 37.5, 40.0, 41.3 kg (P<0.001, s.e. 0.37) for the 70-70%, High-70%, 70%-High, High-High groups respectively. The ratio of parenchyma to total mammary depth was reduced (P=0.043) in response to the nutrition treatments imposed during the second period only. This decrease was by 5.4% in the lambs fed the high nutrition level compared to the 70% nutrition plane fed lambs, indicating the proportion of fat tissue in the gland increased in the high group.

This non-destructive measurement method was able to determine changes in the composition of the young sheep mammary gland related to pre-pubertal nutrition.