Hill country sheep production

Abstract Data from 7,091 straightbred Romney and Border Leicester × Romney ewes grazed at the Whatawhata Hill Country Research Station over the period 1959 to 1967 have been used to obtain estimates of flock and age‐of‐ewe effects on reproduction rate and its components and of year‐to‐year variation. The ewes were from six groups: a Romney control (RCR) flock, a Romney flock in which ewes were mated either to Romney (RER) or to Border Leicester rams (REB), and flocks of first‐cross (F 1 ), second‐cross (F 2 ), and third‐cross (F 3 ) Border Leicester × Romney ewes mated to first‐cross Border Leicester × Romney rams. The ewes' ages at lambing varied from 2 to 5 years and no selection was practised. The ratio of number of lambs weaned per ewe present at lambing increased from the RCR (0.84) to the F 1 (1.07), then declined with interbreeding to the F 2 (0.92) and further to the F 3 (0.87) ewes. Similar changes were evident for the percentage of ewes lambing, of multiple births, and of lambs surviving to weaning. Overall the ratio of number of lambs weaned per ewe present at lambing was 0.71, 0.89, 0.96, and 0.97 for 2‐, 3‐, 4‐, and 5‐year‐olds respectively, the reduced percentage of multiple births having relatively more influence than the other fertility components on the low values for 2‐year‐olds. The ratio of lambs weaned per ewe present at lambing varied between years from 0.73 to 1.08, with a consistent increase from 1964 to 1967. The relative contributions of the three components of reproduction rate to flock, age, and year differences in lambs weaned per ewe present were calculated. Age differences were due to changes in the percentage of ewes lambing, lambs surviving to weaning, and particularly to the proportion of multiple births. Within‐ and between‐flock differences in lambs weaned were due largely to the percentage of multiple births. Differences in ewes lambing and lamb survival rate were also noted between flocks, the Fi being superior in these respects. The lower estimate of lambs weaned per ewe present at lambing for F3 was due largely to a lower proportion of ewes lambing and reduced lamb survival rate. Variation in all three fertility components contributed to between‐year differences in the ratio of lambs weaned per ewe present at lambing, but generally the proportion of multiple births had the most influence.