The effect of the maturity and prior breeding activity of rams and body condition score of ewe hoggets on the reproductive performance of ewe hoggets

The effect of the maturity and prior breeding activity of rams and body condition score of ewe hoggets on the reproductive performance of ewe hoggets
Peer reviewed

Abstract

AIM: To determine the effect of  age and prior use of mature rams at a given ram-to-ewe ratio, and the effect  of body condition on breeding performance and pregnancy rate of ewe hoggets.  
METHODS: Ewe hoggets (n=733) aged  7–8 months were weighed and their body condition scored, then randomly  assigned to one of three treatment groups (Day 0) and joined with either four  two-tooth rams (20 months of age) not used previously (n=244; Two-tooth),  four mixed-aged mature rams that had not been used earlier in the season  (n=244; Mature-fresh), or four mixed-aged mature rams that had been used with  mature ewes immediately prior to joining with hoggets (n=245; Mature-used).  The breeding period was 34 days. Ewe hoggets were identified as having been  marked during the first 17 days only, during both 17-day periods, during the  second 17 days only, or not marked. Hoggets were re-weighed on Day 34, and pregnancy  status determined using ultrasound on Day 92. The breeding soundness of the  rams was assessed on Days –34 and –1.  
RESULTS: Semen samples obtained  from the rams did not differ significantly in any of the parameters measured  (p>0.05). Ewe hoggets joined with Mature-fresh rams were less likely (p<0.05)  to be marked in the second 17 days of breeding only than those joined with  either Two-tooth or Mature-used rams. No other breeding parameters were  affected by breeding group (p>0.05). Hoggets marked in the first 17 days  only were heavier (p<0.05) at Day 0 than those marked in the second 17  days only or not marked. Hoggets diagnosed as twin-bearing were heavier (p<0.05)  than non-pregnant or single-bearing hoggets. Those hoggets marked in the first  17 days only had a greater (p<0.05) body condition score (BCS) than those  marked in the second 17 days only or not marked at all. These differences  were no longer apparent after correction for liveweight (LW).Correction for  LW at Day 0 or change in LW during the breeding period did not affect the  results for breeding performance.  
CONCLUSIONS: Under the conditions  of this study, two-tooth rams and mature rams that had been used previously  were just as suitable as mature rams that had not been used previously for  breeding with ewe hoggets. Further studies are warranted to verify this  result. The re-use of rams without reducing breeding performance would reduce  breeding costs and may make breeding hoggets a more viable option for  farmers. The BCS of ewe hoggets affected breeding performance, and can thus  be used to identify those animals most suitable for breeding.  
KEY WORDS: Breeding  performance, conception rate, pregnancy rate, ewe hogget, ewe lamb, ram, ram  age, liveweight, body condition score

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