Early lifetime performance parameters affecting selection and reproductive success in gilts

The sow replacement rate in Australia is 56.1%, with the average parity at which a sow is culled, currently sitting at 4.1 (Australian Pork Limited 2013). There are several key reasons for premature sow turnover, with failure to express pubertal oestrus and poor reproductive performance during the early parities considered a major cause for removal. Most on farm selection criteria for replacement gilts focus on gilt attributes at selection into the breeding herd. However, including criteria from early lifetime performance parameters such as birthweight, weaning weight, and pre-weaning growth may aid in selecting gilts with a higher probability of reproductive success (Knauer 2016). The hypothesis of this study was gilts that are born heavier and which do not have any growth deficits during the pre-weaning or post-weaning period will have a higher probability of (1) being selected into the breeding herd, and (2) displaying pubertal oestrus, resulting in at least one successful mating

Feeding behaviour traits recorded during gestation are heritable even though feed intake itself is restricted

Data obtained from electronic sow feeders during the gestation period were used to investigate feed intake and feeding behaviour traits from 3785 predominantly (89.9%) F1 sows. Estimates of heritability, permanent environmental effect of the sow and phenotypic variance were obtained for seven distinct time periods during gestation for average feed intake (AFI), daily time spent eating (AFT), rate of feed consumption (AFR), the number of feeding events (AFE) and total born (TB) piglets. As expected, heritability estimates for feed intake traits such as AFI1-AFI7 were not different from zero, which can be explained by the restricted feed allocation (rather than ad libitum feeding). In the same time periods, heritabilities for the amount of time sows spent eating were low to moderate: lowest at the beginning (0.12±0.03) and at the end of gestation (0.16±0.04) and highest in the middle of gestation (range: 0.16 to 0.27). The same pattern was found for the rate of feed consumption. Further investigation of these feeding behaviour traits is warranted with respect to their associations with reproductive performance outcomes, given that they represent potential limitations to sows' ability to consistently meet their nutritional requirements over time

The influence of feed delivery and feeding patterns during gestation on reproductive outcomes for sows

Mid-parent breeding values and outcomes from 6126 mating (4998 farrowing) events and accompanying feed-related traits, derived from feeding events recorded during gestation, were used to investigate the associations between these factors with reproductive outcomes for commercial sows. Variability in genetic merit for piglet birth weight had undesirable consequences for premature sow removal (REM35). Sows in the highest quintile for missed feeding events (> 24 hours between meals) recorded over 90 days had both lower farrowing rate (97.2% vs 97.9 - 99.2%) and increased REM35 (12% vs 7 - 9.5%) compared to the rest. Results from the present study demonstrated that when feeding during gestation did not accommodate variation in litter size and body weight amongst sows, performance of the "average" sow with respect to litter size was favoured. While heritability of intake under restricted feed delivery was zero, variability in litter size alone created heritable variation (h2 ~ 0.05) in actual feed requirement, and therefore the deviation in actual intake from requirement. Reproductive outcomes for commercial sows, and the retention of genetically superior sows for reproductive traits, might be better optimised if gestational feeding was better adapted to sow phenotypes

Direct ovarian-uterine transfer of progesterone increases embryo survival in gilts

This study employed a unilateral ovariectomy model to investigate the relevance of the local supply of progesterone (ovary) compared with the systemic supply of progesterone, in terms of embryo survival in the ipsilateral uterine horn as opposed to the contralateral uterine horn. Thirty gilts were unilaterally ovariectomised (ULO) during the luteal stage of their first oestrous cycle. Half of the ULO gilts were fed at 1.2 maintenance requirement (M), while the other half were fed at 2.4 M. Across ULO gilts 0.8 more embryos survived in the ipsilateral horn compared with the contralateral horn at Day 35 of gestation (P < 0.05). In ULO gilts on the 2.4 M feed level the difference (+1.3; P < 0.05) between the ipsi- and contralateral horn was more pronounced than on the 1.2 M feed level (+0.4; NS). The higher feed level reduced circulating levels of systemic progesterone on Day 5 of pregnancy but not embryo survival at Day 35. However, post-implantation embryo survival was lower on the low feed level. In conclusion, these data indicate that local progesterone supply from the ovaries to the uterus contributes to the probability of embryo survival.R. Z. Athorn, P. Stott, E. G. Bouwman, R. Ashman, S. O’Leary, M. Nottle and P. Langendij

Feeding level and dietary energy source have no effect on embryo survival in gilts, despite changes in systemic progesterone levels

This study was designed to assess the effect of feeding level and dietary energy source on luteal function, systemic progesterone concentration and embryo survival in gilts during early gestation. At Day 0 of pregnancy, 104 gilts were allocated to one of four experimental diets (LStarch: 1.2 × maintenance requirement (M) Starch diet (43.3% starch), n = 31; HStarch: 2.4 × M Starch diet (43.3% starch), n = 21; HFat: 2.4 × M Fat diet (13.5% fat), n = 23; and HFibre: 2.4 × M Fibre diet (7.2% fibre), n = 23). On Day 5 of gestation, no significant difference in circulating concentration of systemic progesterone was seen among the treatments. However, on Day 15 of pregnancy, gilts on the HStarch diet had a significantly lower concentration of systemic progesterone than did gilts on both the LStarch and HFat diets (P < 0.05; 24.8 ± 2.4 v. 32.7 ± 2.4 and 36.1 ± 2.1 ng/mL, respectively). At Day 35 of gestation, there was also a tendency for gilts on the HStarch and HFat diets to have a higher total luteal weight than for gilts on the LStarch diets (7.2 ± 0.2 and 7.1 ± 0.2 v. 6.7 ± 0.2 g (P < 0.05)). No difference in embryo survival was seen among the treatments. From the present study, we can conclude that altering feeding level and dietary energy source did not affect embryo survival, despite the fact that systemic progesterone concentrations were affected on Day 15 of gestation. Also, luteal weight was greater for those gilts on the high feeding level than for those on the low feeding level when fed the same energy source.R. Z. Athorn, P. Stott, E. G. Bouwman, A. C. Edwards, M. A. Blackberry, G. B. Martin and P. Langendij

Undernutrition during early follicle development has irreversible effects on ovulation rate and embryos

This study assessed carry-over effects of energy level during the early antral phase and subsequent follicular phase on follicle recruitment and ovulation rate. Gilts (n = 45) were fed a standard diet to a low (L, ~1.2 kg day–1) or high (H, ~2.7 kg day–1) level during the early antral (luteal) phase, and subsequently fed a H or L feed level during the follicular phase, resulting in four treatment groups (HH, HL, LH and LL). Follicle size at the end of the luteal phase was greater for gilts fed a high feed level previously (3.3 vs 3.0 mm; P < 0.05). During the follicular phase, high feeding increased follicle size at Day 5 (6.9 vs 6.2 mm; P < 0.005) and plasma oestradiol concentration (P < 0.05). Nevertheless, a low feed level during the luteal phase reduced ovulation rate (14.4 vs 13.2; P < 0.05) and embryo number (12.6 vs 10.5; P < 0.05), and this was not counteracted by feed level during the follicular phase. Plasma progesterone concentration after ovulation was lower for LL gilts than for other treatments (P < 0.05). These results indicate that undernutrition during early antral follicle development may have a residual effect on follicle recruitment and quality.T.Y. Chen, P.Stott, R.Z. Athorn, E. G. Bouwman and P. Langendij