In June 2017, Paula Grant from Anexa Vets Raglan started a trial with the objective of evaluating the effect of either oral or injectable copper supplementation of pregnant ewes in terms of liver copper concentration, lambing and weaning percentages and ewe and lamb weights.
While copper deficiency in New Zealand sheep has been demonstrated to cause disease (swayback in lambs – enzootic ataxia, and osteoporosis in lambs and hoggets), there have been few to no published studies evaluating the production effects of subclinical copper deficiency in ewes and lambs.
While supplementation of copper to both cattle and sheep is widespread, we don’t know if supplementing sub-clinically deficient ewes would give a production response. Our trial’s objective was to evaluate the effects of either oral or parenteral copper supplementation of pregnant ewes in terms of liver copper concentration, lambing and weaning percentages, and ewe and lamb weights.
Individually identified pregnant, mature age, Romney stud ewes, from one farm in the Raglan area of New Zealand were enrolled. Following scanning on 5 June 2017, about 60 days prior to start of lambing, pregnant ewes were assigned to 3 treatment groups by undertaking a systematic 3 way draft.
The three groups of 113 to 114 ewes were marked red (control), green (injected with 50 mg of copper as 1 mL of 50mg/mL calcium copper edetate) or white (given a 4g copper oxide capsule). 12 liver biopsies were then taken from each group, and a grass sample was taken. Ewes were also weighed and body condition scored.
Ewes were then run as a single group and the lambs tagged at birth, ewes identified. At docking, 45 days after planned start of lambing, lamb weights were recorded, the ewe liver biopsies repeated, ewes weighed and body condition scored and another grass sample taken.
Lastly at weaning, 120 days after planned start of lambing, all animals’ weights were recorded, the ewes were once again body condition scored, and the grass resampled.
So, what did we do with all this data?
- Firstly, we looked at the ewe groups to ensure they were similar. There was no difference between the age distributions, but the liver concentrations pre-treatment were lower in the injection group, intermediate in the capsule group and highest in the control group. No animals were deficient pretreatment. Because of this, we calculated the difference in the liver copper concentrations. They all declined between scanning and weaning but the decline was greater in the control group than in the capsule and the injection groups – which didn’t differ.
- A note – this seasonal decline in liver copper levels has previously been reported and indicates either significant increase in demand for copper and/or decreased intake or availability. While pasture copper concentrations were within normal range, the pasture iron concentrations were 2 to 4 times higher than the suggested upper normal range and molybdenum concentrations were higher than normal in June, but not later in the year.
- Iron and molybdenum can reduce copper absorption, creating secondary copper deficiency, despite apparently adequate copper intakes. The significant decline in liver copper concentrations across spring, particularly in the control group, may reflect secondary copper ‘deficiency’ associated with the high iron and molybdenum intakes. Despite presence of iron and molybdenum which might have been expected to reduce absorption of the orally administered copper oxide, there was no difference in liver copper concentrations between ewes treated orally compared with those treated by injection. It is not clear why no difference between these treatments was detected.
- Next; numbers of lambs. Numbers of weaned lambs was unaffected by ewe age, and there was no difference between treatment groups in the proportion of lambs weaned. There was also no difference between groups in the number of lambs lost between birth and weaning.
- The average lamb weight across all groups was 35.4kg, and lamb weight was unaffected by ewe age or number of lambs weaned per ewe. There was also no difference in lamb weight between treatment groups.
- Ewe weights – while there was no difference in ewe weights between treatment groups overall, there were some trends worth mentioning. Ewe average daily gain (ADG) was higher overall in those ewes injected with copper, then the control group, then those bolused. Overall, ewes increased weight during pregnancy and then decreased after giving birth.
In conclusion, while supplementing with either oral or injectable copper slows the seasonal rate of decline of liver copper concentrations, it does not create any difference in lambing percentage, weaning percentage, lamb or ewe weights. Thus supplementation with copper without evidence of deficiency is not justified.