Validation of transrectal ultrasonography for assessment of corpora lutea characteristics in pregnant sows and its relationship with litter characteristics at birth1

Abstract

In experiment 1 we investigated the accuracy of transrectal ultrasonography (TUS) to assess the number (OR) and diameter of corpora lutea (CL) in 45 and 25 sows, respectively, at 23.4 ± 2.9 d of pregnancy. The diameter was calculated as the average diameter of 10 biggest CL. Sows were subsequently slaughtered and OR was assessed by dissection of CL from both ovaries (n = 45) and average diameter of the 10 biggest CL was also calculated after measurement of CL with the caliper rule (n = 25). There was a weak relationship between OR counted after dissection of the ovaries and OR counted with TUS (β = 0.28 ± 0.01 CL/CL, P = 0.01), but there was a strong relationship between the average CL diameter measured with the caliper rule after dissection and the average CL diameter based on TUS (β = 1.0 ± 0.1 mm/mm, P < 0.0001). This shows that TUS is not a valid method to assess OR in pregnant sows but it is a valid method to assess average CL diameter. In experiment 2, we investigated the relationship between the average CL diameter assessed by TUS (n = 100) at 23.8 ± 2.4 d of pregnancy and average piglet birth weight (BW) and observed an increase of 37.6 ± 17.8 g in piglet BW per mm increase in average CL diameter measured by TUS (P = 0.04). This relationship is probably because larger CL develop from bigger follicles at ovulation, which might have ovulated oocytes of higher quality that developed into embryos with higher growth potential and thus higher birth weight.

Recent advances in pig reproduction: Focus on impact of genetic selection for female fertility

“…Ovulation rate as found in studies during the last 35 years, showing an increase in 0.2 ovulations per year in both gilts and sows (Da Silva, Broekhuijse, et al., ; Da Silva, Laurenssen, et al., )…”

“…This increased gap is due to increased levels of early and late mortality. Moreover, in gilts (Da Silva, Broekhuijse, et al., ; Da Silva, Laurenssen, et al., ) high ovulation rates were related to higher within litter variation in weight ( ß = 0.01). In sows, high ovulation rates were related with lower placental lengths, where each additional CL represented a decrease in placental length of 0.38 cm at day 35 of pregnancy (Da Silva et al., ).…”

“…The dashed line (‐ ‐ ‐) represents the potential number of embryos (i.e. ovulation rate) (Da Silva, Broekhuijse, et al., ; Da Silva, Laurenssen, et al., ) Legend: The difference between total and vital embryos is considered to be late embryonic mortality, and the difference between ovulation rate and total number of embryos is considered to be early mortality. …”

“…However, both the EBV for piglet birthweight and for within‐litter variation in piglet birthweight had a strong positive association with another ovarian characteristic; average corpus luteum (CL) weight at day 35 of pregnancy (see Table ). In another study, Da Silva, Laurenssen, et al., () used ultrasound to assess the average diameter of the 10 largest CL (five per ovary) at day 20–30 of pregnancy, and related that to subsequent piglet birthweight and standard deviation in piglet birthweight (see Figure ). Each extra mm in CL diameter was related to an increase in average piglet birthweight of 36 g and a standard deviation in piglet birthweight of 24 g. Moreover, an increase in EBV for litter size was related to lower CL weights (Da Silva et al., ).…”

Relations between ovarian & embryonic traits in pigs : effects of genetic selection for litter traits at birth

“…This correlation can also explain the higher average CL weight in gilts with higher EBV for BWSD. Phenotypically, multiparous sows at ~ 3 weeks of pregnancy with an average CL diameter ranging from 9.0 to 10.5 mm had not only a higher average piglet BW but also a higher within litter piglet birth weight variation (318.6 ± 17.0 g) than sows with an average CL diameter ranging from 5.5 to 7.8 mm [252.2 ± 17.9 g, P < 0.05; Da Silva et al (2017b)]. Thus, the increase in average CL weight in gilts with a higher genetic potential for within litter piglet birth weight variation might be a consequence of the genetic association between BW and BWSD.…”