Vital and operational statistics for a Peppin Merino parent stud flock

Abstract

Statistics are presented from a Peppin Merino parent stud on seasonal variation in flock fertility, differences in fertility between rams of various ages, lamb mortality, age composition of the ram pool, and the differential we of rams of various ages. Variation of the percentage of lambs born to ewes served was largely due to seasonal differences in the proportion of ewes (2.5 per cent to 26.5 per cent) with twins. The majority (about 7 per cent) of lamb deaths up to 24 hours after birth was due to natural causes. Total lamb mortality up to 21 days of age was 13 per cent of the number of lambs born. Male lamb mortality up to 24 hours, including lambs born dead, was higher than female mortality (17 per cent u. 6 per cent). Age composition of the ram pool and ram wastage indicated a replacement rate of about 25 per cent. Average age of rams was 4.4 years at the time of birth of their offspring. Ram fertility, assessed as the percentage of ewes lambing to ewes mated, was 55 per cent for two year old, 70 per cent for five year old, and 59 per cent for nine year old rams. From a total of 27 to 37 rams in we each year, 10 favoured rams sired 52 per cent to 70 per cent of lambs alive at 24 hours. These favoured rams were also above average age (5.1 years v. 4.4 years). Thus, favoured sires contribute more heavily to the future flock genotype than other sires; firstly because they have more offspring, and secondly, became pedigree records provide the basis for additional favouritism towards their offspring, especially in the choice of stud ram replacements. This operational pattern has the two-fold disadvantage of increasing the generation intervals relevant to flock replacements and of inefficient exploitation of genetic gains already, made. If, as we believe, this operational pattern is currently typical of the foremost studs of the Merino industry, if is a matter of some concern with respect to the implementation of genetic improvement programmes and the progress expected from them.Where present procedures follow such a pattern thy should be largely reversed so as to use a higher proportion of young rams and to mate them to a much larger proportion of the ewe flock.