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

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.     

Water quality in a serial‐use raceway and its effect on the growth of South African abalone,Haliotis midae Linnaeus, 1758

To quantify the effects of serial‐use of water on abalone growth and feed conversion, this study describes water quality in a serial‐use raceway with seven passes. A flow index of 7.2–9.0 L h^?1 kg^?1 was estimated as the minimum value at which to grow 60–70 mm Haliotis midae, as weight gain (analysis of variance; F_{6, 14}=13.9, P<0.0001) and feed conversion ratio (Kruskal–Wallis test; H_{6, 21}=16.3, P=0.012) were significantly reduced at lower values. pH and dissolved oxygen concentration were positively correlated with the flow index (pH, r²=0.99; P<0.001; dissolved oxygen, r²=0.99; P<0.001), while free ammonia nitrogen (FAN) and nitrite were negatively correlated with the flow index (FAN, r²=0.99, P<0.001; Nitrite, r²=0.93, P<0.001). The concentration of nitrite increased throughout the experiment and may reflect the colonization of Nitrosomonas bacteria as water re‐use increased. Based on comparisons with growth and toxicity tests, it is suggested that low pH combined with growth‐limiting levels of FAN were the first variables limiting abalone growth in the serial‐use raceway.     

Modulation of diversity by grazing and mowing in native tallgrass prairie

Species diversity has declined in ecosystems worldwide as a result of habitat fragmentation, eutrophication, and land-use change. If such decline is to be halted ecological mechanisms that restore or maintain biodiversity are needed. Two long-term field experiments were performed in native grassland to assess the effects of fire, nitrogen addition, and grazing or mowing on plant species diversity. In one experiment, richness declined on burned and fertilized treatments, whereas mowing maintained diversity under these conditions. In the second experiment, loss of species diversity due to frequent burning was reversed by bison, a keystone herbivore in North American grasslands. Thus, mowing or the reestablishment of grazing in anthropogenically stressed grasslands enhanced biodiversity.