Effect of shelter on lamb survival in a high fecundity flock

Abstract

The effect of 3 levels of shelter on perinatal mortality of lambs of Booroola x Coopworth ewes was examined during the lambing period for animals grazing or feeding on ryegrass white clover pastures. Highest survival rate was recorded for partial shelter compared with complete shelter and non shelter treatments.

Death from starvation-exposure during the first 3 days of life was the most important cause of lamb losses where 40 % of all deaths were attributed to this cause. Of the remaining deaths, 22 % occurred within 3 to 4 hours of birth probably due to cold stress, 2 % because of dystocia and no particular causes could be diagnosed for the remaining 36 %. About 58 % of deaths due to starvation-exposure were recorded in the non shelter treatment compared to 21 % in each of the partial and complete shelter treatments indicating the importance of shelter in improving lamb survival. Mean chill index for each shelter treatment was highest in the non shelter treatment (1009 KJ m ⁻² h ⁻¹) indicating that the environment was cooler in this treatment compared to the partial shelter and complete shelter treatments (981 and 879 KJ m ⁻² h ⁻¹ respectively).

Birth weight was the most important factor contributing to lamb survival. There was a highly significant relationship between birth weight and lamb survival. Lamb survival in different birth weight categories of 1-2.5 kg, 2.6-3.5 kg, 3.6-4.5 kg and 4.6-6.0 kg was 40, 80, 84, and 85 % respectively.

Birth rank also significantly affected survival rate, mostly mediated through the birth weight. Survival rates of single, twin, triplet and quadruplet plus quintuplet lambs was about 94, 81, 66 and 51 % respectively.

Lamb survival was higher in younger ewes except for the 3 year old ewe group. Low survival rate in 3 year old ewes (61.2 %) was due to higher losses in the triplet and quadruplet plus quintuplet lambs (46.7 and 55.6 % respectively) in the non shelter treatment.

Lamb sex had no significant effect on lamb survival. Overall survival rate was significantly higher in hairy birth coated compared to fine birth coated lambs (84 vs 67 %).

It was concluded that lamb survival can be improved by providing shelter during the first three days of age.