146 Association Between Gilts and Sows Body Condition and Reproductive Performance

Our objective was to determine the association between gilts and sows body condition (BC) with reproductive performance. Data from 4,543 gilts (PIC Landrace, Hendersonville TN) was collected from January 2017 and July 2019 in a 5,000-sow farm located in Spain. The sow caliper was used to assess BC and was measured in units. Measurements were taken pre-farrowing at d 110 to 113 of gestation and at the day of weaning. Caliper units were used to classify gilt BC at farrowing as thin (< 12), ideal (12–15) and fat (>15). Caliper loss was determined as the caliper units at weaning minus the caliper units pre-farrowing. Response variables included total born, retention rate up to parity 3, total pigs born and total pigs weaned up to parity 3 per gilt served. Tested predictors included BC at farrowing, caliper loss during lactation, number of weaned pigs, lactation length, age at first breeding, wean-to-estrus interval. Data were analyzed with the lm and glm functions from the stats package in R, and final models were selected based on backwards elimination. There was a significant interaction between gilt BC at farrowing and caliper loss in the first lactation. Gilts in ideal condition at farrowing had greater (P < 0.05) retention rate and number of total pigs born and total pigs weaned per gilt served up to parity 3 compared to thin and fat gilts. Fat gilts that lost more than 3 caliper units during lactation had further reduction in retention rate and productivity up to parity 3 compared to fat gilts that lost up to 3 caliper units. For every unit of caliper lost during the first, second, and third lactation, subsequent total born was reduced (P < 0.05) by 0.27, 0.12, and 0.19 pigs, respectively. Results indicated that over-conditioned females are negatively associated with retention and productivity up to parity 3.

OPTIMAL BREEDING AGE FOR THE WEST AFRICAN DWARF SHEEP IN IBADAN

Observations on the age at first breeding of West African Dwarf Sheep at the University of Ibadan. Nigeria showed that the optimal age and weight at 1st breeding of young ewes was not less than eleven months and at least 13kg respectively When mated earlier, the incidence of abortion in­creased and lambs tended to the smaller at birth. In ewes mated at older ages the lengthening of the generation internal was unacceptable. The relalionuship between weight (4 ) and age (X) from four to 56 weeks was estitnated as: Y (kg) = 3.12 + 9.62 x — 0.02 x 2 + 0.0002 x 3 for singles. or Y =2.59 + 0.46 x = 0.01 x2 + 0.0001 x 3 for Mins.

Optimal age of breeding gilts and its impact on lifetime performance

Age at first breeding and lifetime reproductive performance was analyzed on 17,558 F1 Landrace x Yorkshire gilts from 9 piglet producing herds of Midwest, United States entered in herds between 1st Jan 2014 and 31st July 2016. At the time of data collection Dec 2018, 15% of the sows were still active in the herds hence excluded from the analysis. Individual gilt data included date of birth, age in days at first mating, piglet total born by parity, lifetime piglet total born and reason for culling. Quality data checks were done before analysis to eliminate all outlier values together with sows that had no entry information for any listed category. The total database of the sows was classified into 6 classes according to age at the first mating in days 170-190(n=754), 191-211(n=4683), 212-232(n=7123), 233-253(n=3385), 254-274(n=1002) and 275-369 (n=611). Piglet total born obtained from each sow during the lifetime production was significantly (P < 0.05) greater for gilts bred between 233-253 days of age at first mating. Gilts that were bred at <233 days appeared to have a higher risk of removal by farrowing productivity as compared to the other groups. However, the results show that the risk of being culled due to health problems and conformation issues increases as the age at first mating is delayed. Overall reproductive failure appears to be the most economical culling reason across all age groups. There is a need to evaluate the best management decisions for gilt initiation in a herd to maximize her lifetime performance. The results indicate that gilts mated for the first time at the right age, 233–253 days, are more productive, both in lifetime total born and have a minimal risk of culling due to farrowing productivity.

Determining the optimal age of breeding gilts and its impact on lifetime performance, Literature review

Lifetime sow performance is a critical indicator for producers managing a commercial sow herd. It is comprised of sow longevity, lifetime piglets born alive, lifetime number of pigs weaned and lifetime non-productive sow days. Increased lifetime performance and longevity in sows reduces costs of replacement gilts and improves herd performance and profitability (Sasaki et al., 2008, 2011). One of the most critical factors driving the performance of sow herds is gilt management. Decisions regarding gilts have profound effects on sows’ lifetime performance. Age at first breeding of a gilt is a management decision that has been shown to affect performance and retention of the gilt in a herd. The main aim of this review is to establish factors affecting age of first breeding of gilts and its impact on lifetime performance.

Demographic consequences of sexual differences in age at first breeding in Cooper’s Hawks (Accipiter cooperii)

Life-history theory predicts individuals should breed as soon as they are able to reproduce, but many long-lived birds delay breeding. In the Accipitriformes, delayed breeding is the norm, and age when breeding begins is influenced by competing selective pressures. In most Accipitriformes, the reproductive roles of males and females differ; males do most of the foraging and females tend eggs and young. Thus, sexual differences in age at first breeding might be expected, but these differences, possible causes, and implications for individual fitness have received little study. We investigated sexual differences in age at first breeding in a marked population of Cooper’s Hawks (Accipiter cooperii) from 2011 through 2018 in central New Mexico, USA. We hypothesized that males required more experience to pair and breed successfully than females, and we predicted: (1) a lower mean age at first breeding for females than males, and (2) that expected individual fitness of early-breeding males would be lower than for early-breeding females. We found that 79% more females than males bred in their first year (hatching year, HY), and expected individual fitness of HY-breeding females was 21% greater than for HY-breeding males. HY males that attempted to breed settled on nesting territories with exceptionally high prey abundance, nevertheless they experienced 37% lower second-year survival than males that delayed breeding. Females competed for mates based on male age. HY females that paired with relatively older males had 33% higher second-year survival and 16% higher expected individual fitness than HY females that initially paired with relatively younger males. The observed annual rate of growth (λ) of our study population was 1.08, closer to λ predicted by male (1.02) than female (1.21) demographic models. Delayed breeding by males thus had important ramifications for λ, highlighting the need to consider sexual differences in age at first breeding in demographic analyses.

Spurs, sexual dimorphism and reproductive maturity in Tasmanian echidnas (Tachyglossus aculeatus setosus)

We present data from an 18-year study of a wild population of Tasmanian echidnas, which show that the presence of spurs in an adult are a reliable indicator of sex, and that there is a slight but significant sexual dimorphism in size, with a male to female mass ratio of 1.1. Minimum age at first breeding in the wild for Tasmanian echidnas was 5 years, as has been found on Kangaroo Island, compared with 3 years in captive echidnas. It is often assumed that although the echidna is distributed throughout Australia, New Guinea and off-shore islands that all aspects of its basic biology are the same in all populations, but comparisons of our results with data from other populations suggest that there may be differences in size and sexual dimorphism.

Comparison of three different step-down feeding to weaning programmes on performance, body measurements and age at first breeding of Holstein heifers

Performance of female Holstein calves (n = 60) were evaluated in three step-down milk feeding programmes: step-down 1 (STP1: 7.5 litres/day milk from days 1 to 21, 6 litres/day milk from days 22 to 42, 4 litres/day milk from days 43 to 63 and 2 litres/day milk from days 64 to 84 of the study); step-down 2 (STP2; 7.5 litres/day milk from days 1 to 21, 6 litres/day milk from days 22 to 42 and 2 litres/day milk from days 43 to 63 of the study); and step-down 3 (STP3; 7.5 litres/day milk from days 1 to 21, 4 litres/day milk from days 22 to 42 and 2 litres/day milk from days 43 to 63 of the study). Intakes of starter were monitored daily and body weight (BW), average daily gain (ADG) and wither height (WH) were measured monthly. Calves in STP3 had lower dry matter intake between 22 and 42 days than STP2 animals, but starter intake was greater in STP2 and STP3 calves than those in the STP1 treatment between 43–63 and 64–84 days. Total ADG was greater in STP2 and STP3 animals than in STP1 calves. No effect of treatment was observed on breeding age, BW, WH or service per conception. In addition, conception rate at first breeding was not influenced by treatment. It was concluded that the STP2 and STP3 milk feeding regimes improved performance in calves and there was no benefit in feeding milk for longer than 63 days in terms of breeding outcomes.

Evidence for high inter-generational individual quality in yellow-eyed penguins

Longitudinal studies focusing on lifetime reproductive success (LRS) have been used to measure individual breeding performance and identify commonalities among successful breeders. By extending the focus to subsequent generations we identify a proportion of high-quality individuals that contribute disproportionately to the population over multiple generations. We used 23 years of yellow-eyed penguin (Megadyptes antipodes) breeding data from one breeding area to identify the proportion of individual birds that raised successful breeders, which in turn raised offspring. We explored which life-history components influenced LRS, as this knowledge would enable conservation resources to be focused on high-performing individuals in this endangered population. From 2,147 birds marked as chicks, 370 (17.2%) survived to adulthood and recruited to their natal location, of which 219 (10.2%) fledged offspring: 124 (56.6%) of the 219 birds produced offspring that recruited as breeders. Only 102 birds (4.8% of 2,147) fledged first-generation offspring that in turn fledged offspring (second-generation offspring, or grand-offspring). We found that ∼25% of the birds that survived to breed had above-average LRS as well as above-average numbers of grand-offspring, and were more likely to have produced first-generation chicks that recruited and also produced above-average numbers of second-generation chicks. Our findings suggest that there is a core of “super-breeders” that contribute disproportionately to the population over successive generations. Lifespan and age-at-first-breeding were correlated with LRS. We suggest that traits of birds relating to longevity, health (e.g., immunocompetence) and fitness could be examined to identify potential links with high LRS and inter-generational fecundity. “Super-breeders” appear to consistently achieve high LRS and long lifespans in a stochastic environment, demonstrating greater resilience in the face of extreme events.