Do triplet-bearing ewes produce more milk than twin-bearing ewes?
Increasing ewe productivity can be achieved by increasing ewe reproductive rate. A result of this is an increase in triplet-bearing ewes. In a previous post we outlined the challenges faced by the increase in triplet numbers.
One of these challenges was the amount of milk produced by triplet bearing ewes to be able to supply enough milk to feed all three lambs. However, there are not many published studies looking at milk production in triplet rearing ewes.
I have found a study out of the USA and one from NZ that compare the milk production between twin and triplet bearing ewes.
Ewes raising triplets, if they were the same live weight as ewes raising twins, they produced 21% more milk.
Triplet rearing ewes produced 26% more kg of lamb per ewe compared with twin rearing ewes.
There was no difference between milk yield of ewes rearing twins or triplets.
Triplet lambs spent more time grazing pasture than twin lambs.
The first study was published in 1985 and included two different experiments comparing the milk production of twin-rearing ewes and triplet-rearing ewes.
Experiment 1 used 10 crossbred Finn ewes giving birth to twin lambs and 6 ewes giving birth to triplet lambs. Milk production was measured from 21 days after lambing.
Ewes rearing triplets had lower initial weights and lower final weights than the ewes rearing twins. The dry matter intake was similar between treatments.
It appears that the triplet and twin rearing ewes had the same milk production, 3064g and 2728g, respectively. However, once the differences in ewe live weight were accounted for the triplet rearing ewes had greater milk production than the twin rearing ewes on a per weight basis.
The graph below shows the difference in milk production between twin and triplet bearing and rearing ewes adjusted for metabolic live weight. Metabolic live weight is the live weight to the power of 0.75. This takes into account the energy required for maintenance requirements at that live weight. The lower the live weight the lower the maintenance energy requirements.
Experiment 2 used 9 ewes giving birth to triplet lambs, at lambing 4 of these ewes had one lamb removed from them so that 4 ewes reared twins and 5 ewes reared triplets.
The graph below shows the difference in milk production between triplet bearing ewes that reared either twins or triplets adjusted for metabolic live weight, similar to that in experiment 1. The twin rearing ewes gained more live weight across lactation than the ewes rearing triplets.
The authors suggested that the greater milk production could have been a result of increased mammary stimulation from the extra lamb. However, another thing to note with these two studies is the small number of ewes used in each treatment group. Even one of the ewes in either treatment having greater milk production would greatly influence the treatment average. Therefore it is difficult to draw conclusions from just this study.
The next study is based in NZ and compared milk production between twin- and triplet-rearing ewes and grazing time between twin and triplet lambs.
Milk yield of ewes with twin (n=13) and triplet (n=8) lambs, grazing pasture in spring was measured at four, seven and ten weeks after lambing.
As shown in the graph below, there was no difference between milk yield of ewes rearing twins or triplets at day 28, 49 or 70 of lactation. This means that on a per lamb basis, triplet lambs had less milk compared with twin lambs.
As a result of this outcome, the time spent grazing was measured to determine if triplet lambs compensated for the lower milk intake by grazing more pasture.
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The behaviour of the lambs were observed across two, 2hr periods (one morning, one afternoon) each week from week 3 to week 9 of lactation. The behaviours recorded were grazing and suckling. The time spent grazing by triplets (39.4±1.94 % on lactation day 29) was significantly greater than the time spent grazing by twins (37.7±1.94% on lactation day 29) across the 4 hours the behaviour measurements were recorded.
Overall, triplet lambs spent more time grazing than twin lambs, however, triplet lambs grew significantly less than twin lambs gaining 14.9 kg compared to 17.0 kg, respectively.
So although triplet lambs spent more time grazing than twins, this did not compensate for the lower milk allocation, therefore, triplets suffer a relative lack of available milk compared to twins and are not able to compensate for this by increasing time grazing.
This study had 21 ewes total which was more than that of the first study. More measurements is always better, however, milk yield is a time consuming trait to measure so limits the number of measurements able to be taken within a similar time period. The method of milk collection in both these studies was using the “oxytocin method" first described by McCance & Alexander
(1959). The technique involves i.v. injection of oxytocin V (Vetpharm LTD) then emptying the udder by machine and hand milking, and repeating the milking procedure a measured time (about 3-6 h) later, at which time the milk yield is measured. A sample (~20 ml) was collected from each ewe at the afternoon milking. The lambs were separated from the ewes (and bottle fed as required) during the 6-h period.
This study provides evidence that triplet lambs do not receive enough energy and nutrients from milk alone and would likely benefit from a milk supplement or high quality feed if possible as triplet lambs can not compensate with grazing pasture.
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Peterson, S. W. (2006). Do ewes with twin and triplet lambs produce different yields of milk and does the grazing behaviour of their lambs differ?. Proceedings of the New Zealand Society of Animal Production, 66, pg444.