REPRODUCTIVE PERFORMANCE OF CROSSBRED EWES SELECTED FOR FALL VS SPRING LAMBING UNDER RANGE OR FARM FLOCK MANAGEMENT SYSTEMS (PROGRESS REPORT)

SUMMARY

Reproductive performance is reported for fall and spring lambing flocks under both range (Antelope Range Livestock Station, Buffalo, SD) and farm flock (SDSU Sheep Unit, Brookings, SD) management systems. Significant improvement was seen for fall lambing in the range system. The percent of ewe lambs that were exposed to lamb in the fall at 12-13 months of age that lambed was higher in 1998 than 1997 in the farm flock system. Selection for fall lambing traits will continue. In addition, blood samples have been collected for analyses of genetic markers that may speed selection progress.

INTRODUCTION

Many products and procedures have been attempted over a period of years aimed at producing lambs out of the normal (spring) lambing season. The reasons for the desire to have out of season lambs are as varied as the sheep industry. Some prefer non-traditional lambing time for show/sale purposes, some for convenience (better weather, labor schedules, etc.) and most importantly, some to provide a more continuous supply of fresh lambs on the market. Extending the lambing season provides opportunity for better use of facilities, more efficient use of labor, more consistent lamb numbers to the packer and a more consistent, high quality product for the consumer.

This study was initiated to evaluate the results of selecting for fall lambing under two management systems, farm vs range.

EXPERIMENTAL PROCEDURES

Finn-Dorset x Targhee (FDT, n=524) and Hampshire x FDT (n=80) ewe lambs produced at the Antelope Range Livestock Station (Buffalo, SD) in 1992, 1993, and 1994 are the base flock of this study. These April-born ewe lambs were weaned in August-September and transported to the Brookings Station where they were managed until exposure at approximately 12 months of age for September lambing. Each year the pregnant ewes from this initial exposure were randomly assigned to either the range or farm flock fall lambing group. The remaining open ewes were randomly split between the four lambing groups to balance the numbers per group, i.e., approximately 50 ewes entering the fall and spring groups in the range and farm flock systems each year. Starting with the fall 1994 born group of lambs, subsequent replacement ewes were selected from multiple birth, early lambing ewes and remained with their birth group (fall born ewe lambs remain with the fall group and spring born ewe lambs remain with the spring group). Rams were selected for the fall lambing groups at both locations and were used as yearlings for one year (both fall and spring) at their respective locations. Rams were replaced annually and the ewes were turned over as rapidly as possible while maintaining base flock numbers. The spring group served as the control.

Common practices to all groups included the use of teaser rams for 15 days prior to exposure to fertile rams, flushing, a 35 day breeding season and routine vaccinations. Ewes remained with their lambing group unless they missed two consecutive lambings, were culled for unsoundness (i.e. lameness, bad udders, prolapse), death, or age. After the flock size was established, ewe turnover was as rapid as possible with approximately one-third of the ewes being replaced each year. Each flock was maintained at approximately 150 head at each lambing opportunity.

At lambing, number of lambs born (live and dead), lamb sex, and individual lamb weight were recorded. Ewes were allowed to raise no more than two lambs. Extra lambs were either grafted onto another ewe or were sold as orphan lambs if no graft dam was available. In both spring flocks, all male lambs were castrated, while in the fall flocks 10 to 12 male lambs were left intact as possible ram replacements. Other data collected were numbers of ewes exposed, lambing, and weaning a lamb. Pre-breeding weight and condition score of ewes were also recorded.

RESULTS AND DISCUSSION

Lambing performance for mature ewes is shown in Table 1. The percentage of ewes lambing in the fall of 1998 at Brookings was 60%, considerably lower than the previous three fall groups. A management error resulted in the loss of 107 ewes from the fall 1998 Brookings group.