Direct and correlated responses to selection for autumn lambing in sheep

Background Seasonal reproduction limits productivity, flexibility, and profitability in commercial sheep production. Hormonal and (or) photoperiodic manipulation can be used to control estrous cycles in sheep and reduce limitations that are imposed by the seasonal anestrous but are often impractical or incompatible with the extensive management systems preferred for ruminant livestock. Thus, the current study investigated the use of selection to improve realized fertility (i.e., the proportion of ewes that lambed) following an out-of-season spring joining period (May and June) in a crossbred sheep population. Results Over 17 years, estimated breeding values (EBV) for fertility in selected (S) ewes increased by 0.175 (0.01 per year). The mean EBV for fertility of S ewes was greater than that of control ewes by year 10 (P = 0.02), and the fertility of adult (≥ 3 years old) ewes reached 0.88 ± 0.05 by year 17. Lambing began approximately 140 days after the introduction of rams, and 64% of the S ewes that lambed did so in the first 17 days of the potential lambing season, which indicated that most of the S ewes were cycling at the time of ram introduction and were not induced to cycle by the introduction of breeding males (i.e., the so-called “ram effect”). Animals in the S line had modest increases in body weight and scrotal circumference. A modest negative trend in the additive maternal effect on birth weight was observed but was reversed by additional selection on EBV for maternal birth weight. The heritability of litter size in autumn lambing was low (0.04) and could potentially limit the response to selection for this trait. Conclusions Selection improved realized ewe fertility in out-of-season mating, with absolute increases of approximately 1% per year in the percentage of joined ewes that lambed in the autumn. Genetic antagonisms with other performance traits were generally small. A modest antagonism with maternal breeding values for birth weight was observed but it could be accommodated by selection on EBV for maternal birth weight. Our results support results of previous studies that indicate that these selected ewes had one of the shortest seasonal anestrous periods reported for temperate sheep breeds and that spring-lambing lactating ewes from the selection line were capable of relatively rapid rebreeding in the spring.

Film Cooling Experimental Study on Sinusoidal Corrugated Liner for Afterburner

The need of improved cooling effectiveness for hot components in jet engines has led to new designs of afterburner liners. In the present paper, experiments were performed to reveal the cooling characteristics and flow loss of various sinusoidal corrugated liners for an advanced afterburner. It is found that there are alternate high temperature and low temperature zones corresponding to the wave crests and troughs of the corrugated liner, respectively. Compared to the flat liner, the corrugated liner increases cooling effectiveness by 10 % at the blowing ratio of 0.5, by 4.5 % at the blowing ratio of 3.2. However, the difference in discharge coefficients for these two kinds of liners is only 4.3 %. The increased opening ratio of film holes from 1.42 % to 3.72 % for corrugated liners is able to improve the cooling effectiveness by 9.8 %. However, the discharge coefficient is decreased by 34.1 %. The augment of amplitude of liners can enhance the ram effect of cooling air, which has an advantage to increase the local blowing ratio, and to form good cooling film at the windward of wave troughs. The flow loss is bigger while the cooling effectiveness is enhanced due to the change of amplitude of the liner.