Prenatal heat stress reduces male anogenital distance at birth and adult testis size, which are rescued by concurrent maternal Artemisia absinthium consumption.

Boars from sows with elevated plasma cortisol during pregnancy have shorter anogenital distance (AGD), a trait associated with subfertility. Since gestating sows often experience summer heat stress (HS), a mouse model was used to evaluate the effect of prenatal HS on AGD and fertility; efficacy of the heat stress-mitigating supplement Artemisia absinthium (AB) was also evaluated. Dams were treated from d 8-18 of gestation, residing in ambient temperatures from 0700 to 1900h. From 1900 to 0700h females were exposed to 34.13±0.27°C (HS) with access to water (HSW; n=9), HS with access to a 1% w/v decoction of AB (HSA; n=9), 20.81±0.20°C (thermal neutral; TN) with water (TNW; n=10) or TN with AB (TNA; n=10). Daily liquid consumption was measured from d 6-18, and tail temperature was recorded at 0700 and 1900h from d 8-18. Progeny weight and AGD were recorded at birth and weaning. At maturity, males were mated to non-littermate females from each treatment; these females were euthanized after 16 d of TN gestation. Reproductive traits were compared among all male/female treatment combinations; testes were weighed. Average liquid intake differed among treatments with HS and AB animals drinking more (P<0.0004). A treatment by time interaction for tail temperature (P<0.001) was observed; HS increased tail temperature of HSA and HSW animals similarly compared to TNA and TNW. Treatment affected (P<0.01) male birth AGD (HSW shortest; P<0.07). At maturity, HSW males also had the smallest testes (P<0.02). However, we observed no differences in fertility (P>0.10). These data indicate that in utero HS decreases both male birth AGD and adult testis size, effects which maternal AB consumption mitigates.

Plenary contribution to International Conference on Boar Semen Preservation 2011. Genetic selection for freezability and its controversy with selection for performance.

Little data are available in the literature regarding freezability of boar sperm or its relationship with other traits. Existing data suggest the trait would respond favourably to selection, and information is available from other species suggesting components that might have changed. Genetic parameters are estimated for boar sperm freezability including heritability and correlations with other production traits. Sperm freezability is an ideal candidate for marker assisted-selection or selection for favourable alleles.

Genetic selection of boars.

Selection of boars by visual appraisal is the simplest and oldest method used by the swine industry. However, individual performance testing, and later use of computers to incorporate relatives' data and account for environmental variation, resulted in greater rate of improvement for economically important traits. Examples of molecular genetic tools that have increased improvement for some traits are also discussed. Accurate identification of genetic merit is increasingly important with widespread use of AI and resultant greater progeny number per sire. Historically, selection was to produce desirable progeny; however, with the majority of boars now housed in dedicated boar facilities, and the efficiency of sperm production being recorded, boar stud personnel are increasingly interested in selection of boars for fertility traits. Selecting boars that are lean and heavily muscled and have good semen parameters may be problematic, given the genetic relationships among the traits. Whereas conventional animal breeding methods will remain important, use of molecular tools will increase, and identification of a boar's fertility potential at birth will allow earlier and more efficient selection of high-fertility boars. Ability to achieve acceptable female reproduction with frozen semen would facilitate selection for longevity. However, this would lengthen the generation interval and could dilute selection intensity for other traits, as it requires indirect selection for semen freezability.

Arachidonate 15-lipoxygenase and ubiquitin as fertility markers in boars.

Accurate semen analysis is an important issue in the swine industry. We evaluated two candidate fertility marker proteins associated with sperm cytoplasmic droplet (CD), including 15-lipoxygenase (15-LOX) and ubiquitin (UBI) in a controlled single-sire artificial insemination (AI) trial. Ejaculates (n=116) were collected from 18 fertile Large White boars monthly for 8 mo, and analyzed by semi-quantitative, densitometry-based Western blotting and flow cytometry with antibodies against 15-LOX and UBI. Data were correlated with farrowing rates (FR) and total numbers of piglets born (TNB) from 1754 AI services by 13 of 18 boars, and compared with a conventional microscopic semen analysis. In semi-quantitative Western blotting, both 15-LOX and UBI were correlated with seasonal changes in the percentage of normal (r=-0.38, P<0.01; r=-0.27, P<0.05, respectively) and CD-bearing spermatozoa (r=0.35, P<0.01; r=0.27, P<0.05, respectively). In flow cytometry, UBI and 15-LOX levels showed seasonal changes coinciding with seasonal changes of FR and TNB, representing 13 boars, 88 ejaculates and 1,232 AI services. There were correlations between flow cytometric values of UBI and FR (r=0.31; P<0.05), adjusted FR (r=0.30; P<0.05), TNB (r=-0.38; P<0.01) and adjusted TNB (r=-0.37; P<0.01). Flow cytometric measurements of 15-LOX correlated negatively with TNB (r=-0.33; P<0.05) and adjusted TNB (r=-0.34; P<0.05). These data suggested that boar fertility estimation could be achieved within a group of fertile boars by the use of objectively measurable fertility markers. Flow cytometry appeared more informative and more practical than semi-quantitative Western blotting. This technology could be further optimized for the selection of the most fertile sires in an artificial insemination program.

Determining the effects of early gestation in utero heat stress on postnatal fasting heat production and circulating biomarkers associated with metabolism in growing pigs.

The study objective was to characterize effects of early gestation in utero heat stress (IUHS) on postnatal fasting heat production (FHP) and blood biomarkers associated with metabolism in growing pigs. Based on previous observation of increased postnatal core body temperature set point in IUHS pigs, we hypothesized that FHP would be altered during postnatal life because of IUHS. Pregnant first-parity gilts were exposed to thermoneutral (TN; = 4; 17.8 ± 0.1°C) or heat stress (HS; = 4; cyclical 28 to 38°C) conditions from d 30 to 60 of gestation. At weaning (21 d of age), 2 median-weight male pigs (1 barrow and 1 boar) were selected from each litter ( = 8 in utero TN [IUTN] and 8 IUHS pigs) and then housed in TN conditions based on age. Blood samples were collected at 8, 9, and 10 wk of age when pigs were in a fed state to analyze thyroxine (T4) and triiodothyronine (T3) concentrations. Pigs were trained to enter an indirect calorimeter from wk 8 through 10 of life and then acclimated over a 24-h period 1 wk prior to testing. At 12 wk of age, pigs were fasted for 24 h, and then indirect calorimetry was performed on individual pigs over a 23-h testing period to determine FHP and the respiratory quotient in 3 intervals (0900 to 1700 h, 1700 to 0000 h, and 0000 to 0800 h). Body weight was determined before and after testing and was similar for all pigs ( = 0.77; 37.0 ± 0.5 kg BW). Data were analyzed using PROC MIXED in SAS 9.4. No boar vs. barrow differences were observed with any analysis. Overall, FHP per kilogram BW was greater ( = 0.03; 12.1%) in IUHS pigs compared with IUTN pigs. Fasting heat production per kilogram BW was greater ( < 0.01; 19.8%) from 0900 to 1700 h compared with 1700 to 0000 h and 0000 to 0800 h and was greater (10.9%) from 1700 to 0000 h compared with 0000 to 0800 h. The RQ did not differ by in utero treatment ( = 0.51; 0.72 ± 0.01); however, the RQ was increased ( < 0.01; 13.0%) from 1700 to 0000 h compared with 0900 to 1700 h and 0000 to 0800 h. No other FHP and RQ differences were detected. Although no in utero treatment differences were observed for T4 ( = 0.11; 52.2 ± 6.2 ng/mL), T3 was greater overall ( = 0.04; 19.5%) in IUHS pigs than in IUTN pigs. In summary, FHP and circulating T3 were increased in IUHS pigs, and this may have implications for postnatal production efficiency in pigs gestated during hot summer months.

In utero heat stress increases postnatal core body temperature in pigs.

In utero heat stress (IUHS) negatively impacts postnatal development, but how it alters future body temperature parameters and energetic metabolism is not well understood. Future body temperature indices and bioenergetic markers were characterized in pigs from differing in utero thermal environments during postnatal thermoneutral (TN) and cyclical heat stress (HS) exposure. First-parity pregnant gilts ( = 13) were exposed to 1 of 4 ambient temperature (T) treatments (HS [cyclic 28°C to 34°C] or TN [cyclic 18°C to 22°C]) applied for the entire gestation (HSHS, TNTN), HS for the first half of gestation (HSTN), or HS for the second half of gestation (TNHS). Twenty-four offspring (23.1 ± 1.2 kg BW; = 6 HSHS, = 6 TNTN, = 6 HSTN, = 6 TNHS) were housed in TN (21.7°C ± 0.7°C) conditions and then exposed to 2 separate but similar HS periods (HS1 = 6 d; HS2 = 6 d; cycling 28°C to 36°C). Core body temperature (T) was assessed every 15 min with implanted temperature recorders. Regardless of in utero treatment, T increased during both HS periods ( = 0.01; 0.58°C). During TN, HS1, and HS2, all IUHS pigs combined had increased T ( = 0.01; 0.36°C, 0.20°C, and 0.16°C, respectively) compared to TNTN controls. Although unaffected by in utero environment, the total plasma thyroxine to triiodothyronine ratio was reduced ( = 0.01) during HS1 and HS2 (39% and 29%, respectively) compared with TN. In summary, pigs from IUHS maintained an increased T compared with TNTN controls regardless of external T, and this thermal differential may have practical implications to developmental biology and animal bioenergetics.

Effects of in utero heat stress on postnatal body composition in pigs: I. Growing phase.

Environmentally induced heat stress (HS) negatively influences production variables in agriculturally important species. However, the extent to which HS experienced in utero affects nutrient partitioning during the rapid lean tissue accretion phase of postnatal growth is unknown. Study objectives were to compare future whole-body tissue accretion rates in pigs exposed to differing in utero and postnatal thermal environments when lean tissue deposition is likely maximized. Pregnant sows were exposed to thermoneutral (TN; cyclical 15°C nighttime and 22°C daytime; n = 9) or HS (cyclical 27°C nighttime and 37°C daytime; n = 12) conditions during their entire gestation. Twenty-four offspring from in utero TN (IUTN; n = 6 gilts and 6 barrows; 30.8 ± 0.2 kg BW) and in utero HS (IUHS; n = 6 gilts and 6 barrows; 30.3 ± 0.2 kg BW) were euthanized as an initial slaughter group (ISG). Following the ISG, 48 pigs from IUTN (n = 12 gilts and 12 barrows; 34.1 ± 0.5 kg BW) and IUHS (n = 12 gilts and 12 barrows; 33.3 ± 0.3 kg BW) were exposed to constant HS (34.1 ± 2.4°C) or TN (21.5 ± 2.0°C) conditions until they reached 61.5 ± 0.8 kg BW, at which point they were sacrificed and their whole-body composition was determined. Homogenized carcasses were analyzed for N, crude fat, ash, water, and GE content. Data were analyzed using PROC MIXED in SAS 9.3. Rectal temperature and respiration rate increased (P < 0.01) during postnatal HS compared to TN (39.4 vs. 39.0°C and 94 vs. 49 breaths per minute, respectively). Regardless of in utero environment, postnatal HS reduced (P < 0.01) feed intake (2.06 vs. 2.37 kg/d) and ADG (0.86 vs. 0.98 kg/d) compared to TN conditions. Postnatal HS did not alter water, protein, and ash accretion rates but reduced lipid accretion rates (198 vs. 232 g/d; P < 0.04) compared to TN-reared pigs. In utero environment had no effect on future tissue deposition rates; however, IUHS pigs from the ISG had reduced liver weight (P < 0.04; 17.9%) compared to IUTN controls. In summary, postnatal HS reduced adipose tissue accretion rates, but IUHS did not appear to impact either lean or adipose tissue accretion during this specific growth phase.

Effects of in utero heat stress on postnatal body composition in pigs: II. Finishing phase.

The detrimental effects of heat stress (HS) on animal productivity have been well documented. However, whether in utero HS interacts with a future thermal insult to alter tissue deposition during the finishing phase of pig growth is unknown. Study objectives were to compare the subsequent rate and quantity of whole-body tissue accretion in pigs exposed to differing in utero and postnatal thermal environments. Pregnant sows were exposed to thermoneutral (TN; cyclical 15°C nighttime and 22°C daytime; n = 9) or HS (cyclical 27°C nighttime and 37°C daytime; n = 11) conditions during their entire gestation. Twenty-four offspring from in utero TN (IUTN; n = 6 gilts and 6 barrows; 62.4 ± 0.7 kg BW) and in utero HS (IUHS; n = 6 gilts and 6 barrows; 61.9 ± 0.8 kg BW) were euthanized as part of an initial slaughter group (ISG). After the ISG, 48 pigs from IUTN (n = 12 gilts and 12 barrows; 66.1 ± 1.0 kg BW) and IUHS (n = 12 gilts and 12 barrows; 63.4 ± 0.7 kg BW) were exposed to constant HS (34.4 ± 1.8°C) or TN (22.7 ± 2.5°C) conditions until they reached 80.5 ± 1.5 kg BW, at which point they were sacrificed and their whole-body composition was determined. Homogenized carcasses were analyzed for N, crude fat, ash, water, and GE content. Data were analyzed using PROC MIXED in SAS 9.3. Rectal temperature and respiration rate increased during postnatal HS compared to TN (39.6 vs. 39.3°C and 92 vs. 58 breaths per minute, respectively; P < 0.01). Postnatal HS decreased (P < 0.01) feed intake (2.13 vs. 2.65 kg/d) and ADG (0.70 vs. 0.94 kg/d) compared to TN conditions, but neither variable was influenced by in utero environment. Whole-body protein and lipid accretion rates were reduced in HS pigs compared to TN controls (126 vs. 164 g/d and 218 vs. 294 g/d, respectively; P < 0.04). Independent of postnatal environments, IUHS reduced future protein accretion rates (16%; P < 0.01) and tended to increase lipid accretion rates (292 vs. 220 g/d; P < 0.07) compared to IUTN controls. The ratio of lipid to protein accretion rates increased (95%; P < 0.01) in IUHS pigs compared to IUTN controls. In summary, the future hierarchy of tissue accretion is altered by IUHS, and this modified nutrient partitioning favors adipose deposition at the expense of skeletal muscle during this specific phase of growth.

Carcass composition of market weight pigs subjected to heat stress in utero and during finishing.

Objectives were to investigate the effects of prolonged gestational and/or postnatal heat stress on performance and carcass composition of market weight pigs. Pregnant gilts were exposed to gestational heat stress (GHS, 28°C to 34°C, diurnal) or thermal neutral (18°C to 22°C, diurnal) conditions during the entire gestation or during the first or second half of gestation. At 14 wk of age (58 ± 5 kg), barrows were housed in heat stress (32°C, HS) or thermal neutral (21°C, TN) conditions. Feed intake and BW were recorded weekly, and body temperature parameters were monitored twice weekly until slaughter (109 ± 5 kg). Organs were removed and weighed, and loin eye area (LEA) and back fat thickness (BF) were measured after carcass chilling. Carcass sides were separated into lean, separable fat, bone, and skin components and were weighed. Moisture, lipid, and protein content were determined in the LM at the 10th rib. Data were analyzed using a split plot with random effect of dam nested within gestational treatment. Carcass measurements included HCW as a covariate to control for weight. Planned orthogonal contrast statements were used to evaluate the overall effect of GHS in the first half, second half, or any part of gestation. Gestational heat stress did not alter postnatal performance or most body temperature parameters (P > 0.10). However, ADFI in the finishing period was increased (P < 0.05) in response to GHS, particularly in pigs receiving GHS in the first half of gestation. Gestational heat stress during the first half of gestation decreased head weight as a percent of BW (P = 0.02), whereas GHS in the second half of gestation decreased bone weight as a percent of BW (P = 0.02). Heat stress reduced ADG, BW, and HCW (P < 0.0001). Lean tissue was increased in HS pigs on both a weight and percentage basis (P < 0.0001), but LEA was similar to TN carcasses (P = 0.38). Carcasses from HS barrows also had less carcass separable fat (P < 0.01) and tended to have less BF (P = 0.06) compared with those from TN barrows, even after controlling for HCW. However, percent intramuscular fat did not differ between treatments (P = 0.48). The LM from HS carcasses had a greater moisture to protein ratio (P = 0.04). HS barrows also had decreased heart (P < 0.001) and kidney (P < 0.0001) as a percent of BW compared with TN pigs. In summary, GHS may affect head and bone development, subsequently affecting carcass composition. Chronic HS during finishing results in longer times to reach market weight and a leaner carcass once market weight is achieved.

Short- and long-term influence of perinatal dexamethasone treatment on swine growth.

The objective was to evaluate the effects of perinatal dexamethasone (Dex) treatment on postnatal growth in pigs. Experiment 1: 42 piglets were assigned according to birth weight and sex to receive either Dex (1 mg/kg body weight) or sterile saline (Control; equivalent volume) i.m. within 1h of birth. Body weights were recorded weekly and at sacrifice (day 18). Birth weights (1.43 +/- 0.05 kg) did not differ between treatment groups (P > 0.19). At day 18, Dex pigs were heavier than Control pigs (5.46 +/- 0.24 and 4.45 +/- 0.26 kg, respectively). Serum IGF-1 was 17.3% higher in Dex pigs (P < 0.04) compared to Controls. For serum GH, there was a treatment x sex interaction (P < 0.04) with GH being 51% lower in Dex males compared to Control males, and no differences in females. Experiment 2: 71 pigs were assigned according to birth weight and sex to receive either Dex (2 mg/kg body weight) or sterile saline (Control; equivalent volume) i.m. within 1 h of birth. Body weights were recorded weekly until weaning (day 21) and then every 14th day until market weight. Birth weights (1.53 +/- 0.03 kg) did not differ (P > 0.35) between treatment groups or sexes. Dexamethasone increased growth from birth to market weight by 4.15%. Carcass weights were not different (P > 0.34) between Dex (89.9 +/- 1.17 kg) and Control pigs (88.6 +/- 1.36 kg). Overall, Dex enhanced growth in pigs from birth to market weight with minimal effects on carcass and meat quality.

A model for economic comparison of swine insemination programs.

Optimal artificial insemination schedules are those that result in a high farrowing rate and litter size, while minimizing costs of semen and labor by avoiding unnecessary inseminations. A simulation model programmed in a commercial spreadsheet was developed to permit comparison of alternative schedules. Farrowing rate and litter size for a particular schedule were dependent on the timing of insemination relative to the time of ovulation. Economic return was calculated by multiplying the number of pigs born per bred sow by $33.00 and subtracting the cost of producing a litter of pigs and raising them to weaning ($222.88 per sow plus $2.44 per pig born) and the cost of detection of estrus and breeding. Seven insemination schedules combined with once versus twice per day detection of estrus were simulated in 500 herds of 100 sows each. Inseminations were simulated to occur on schedules of: 1) 0, 12, 24 and 36 h; 2) 12, 24 and 36 h; 3) 0 and 24 h; 4) 12 and 36 h; 5) 12 h; 6) 24 h; and 7) 36 h after first detection of estrus. Schedule 1 was predicted to yield the highest farrowing rate and litter size. Economic return was highest for Schedule 2 with twice per day detection of estrus followed closely by Schedule 1 with once per day detection of estrus at $14.90 and $13.75 per bred sow, respectively. High performance was dependent on insuring that inseminations occurred at an optimum time in as great a proportion of sows as possible.

Factors affecting follicular populations on Day 3 postweaning and interval to ovulation in a commercial sow herd.

Sows (n=146) in a commercial herd were studied to determine factors affecting follicular populations and interval to ovulation after weaning. Ovaries were examined daily by ultrasonography beginning on Day 3 postweaning and twice daily from Day 4.5 until ovulation. Ovarian images were recorded on videotape on Day 3 postweaning and follicles were counted. Subsequent ultrasounds were used to determine time of ovulation. Sows with short weaning to ovulation intervals (or=9 days) weaning to ovulation intervals (P<0.001). Follicular populations in sows with intermediate (7-8.5 days) intervals to ovulation were intermediate in diameter when compared to sows with short or long intervals to ovulation. Parity and body condition score (BCS) affected interval to ovulation; first parity and low body condition sows had longer intervals to ovulation (P<0.001 and 0.05, respectively). The longer intervals to ovulation in first parity and low body condition sows were associated with lesser follicular diameters on Day 3 after weaning. We conclude that follicular populations measured by ultrasonography on Day 3 after weaning were different for sows with different intervals to ovulation. Furthermore, production factors (i.e. parity and BCS) known to influence interval to ovulation were associated with differences in follicular growth within the first 3 days after weaning in sows.

Effect of time of ovulation and sperm concentration on fertilization rate in gilts.

In normal production practices, sows and gilts are inseminated at least twice during estrus because the timing of ovulation is variable relative to the onset of estrus. The objective of this study was to determine if a normal fertilization rate could be achieved with a single insemination of low sperm number given at a precise interval relative to ovulation. Gilts (n=59) were randomly assigned to one of three treatment groups: low dose (LD; one insemination, 0.5 x 10(9) spermatozoa), high dose (HD; one insemination, 3 x 10(9) spermatozoa) or multiple dose (MD; two inseminations, 3 x 10(9) spermatozoa per insemination). Twice daily estrus detection (06:00 and 18:00 h) was performed using fenceline boar contact and backpressure testing. Transrectal ultrasonography was performed every 6 h beginning at the detection of the onset of standing estrus and continuing until ovulation. Gilts in the LD and HD groups were inseminated 22 h after detection of estrus; MD gilts received inseminations at 10 and 22 h after detection of estrus. Inseminations were administered by using an insemination catheter and semen was deposited into the cervix. The uterus was flushed on Day 5 after the onset of estrus and the number of corpora lutea, oocytes, and embryos were counted. Time of insemination relative to ovulation was designated as 40 to >24 h, 24 to >12 h, and 12 to 0 h before ovulation and >0 h after ovulation. The LD gilts had fewer embryos (P<0.04), more unfertilized oocytes (P<0.05) and a lower fertilization rate (P<0.07) compared to MD gilts. The effects of time of insemination relative to ovulation and the treatment by time interaction were not significant. We conclude that a cervical insemination with low spermatozoa concentration may not result in acceptable fertility even when precisely timed relative to ovulation.

Use of melengestrol acetate and gonadotropins to induce fertile estrus in seasonally anestrous ewes.

Ewes of three genotypes (Hampshire, n = 59; Rambouillet, n = 36; crossbred, n = 57) were used to determine the efficiency of melengestrol acetate (MGA) and(or) PG-600 (a combination of pregnant mare's serum gonadotropin and human chorionic gonadotropin) in inducing fertile estrus in seasonally anestrus ewes. Ewes were assigned randomly, within genotype, to treatments in a 2 x 2 factorial arrangement. Treatments were control, .125 mg of MGA given twice per day for 9 d (MGA), a single 5-mL injection of PG-600 (PG-600), and the combination of treatments MGA and PG-600 (MGA/PG-600). Feeding of MGA began on May 14, 1990, and ended on May 23. Injections of PG-600 were given immediately after the last feeding of MGA or vehicle on May 23. All ewes were exposed to fertile, brisket-painted rams on May 24 (d 0) for 40 d. Ewes were checked for estrus twice daily for 9 d. Laparoscopy was performed, to assess ovulation rate (OR), on d 6 for ewes that were not detected in estrus and on d 12 for ewes that exhibited estrus. Percentage of ewes mated was increased by MGA (P less than .001). Ovulation rate of ewes exposed to rams was increased by PG-600 (P less than .01) and this effect was enhanced by MGA (P less than .05), whereas MGA alone tended to decrease OR (P less than .10). Melengestrol acetate decreased the interval to lambing by 6.5 d (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Correlated response in placental efficiency in swine selected for an index of components of lifter size.

The objective of this study was to evaluate correlated response in placental efficiency to selection for components of litter size. Fourteen generations of selection had resulted in a difference between lines of three fully formed piglets at birth. Gilts from a line selected for an index of components of litter size (S, n = 33) and a randomly selected control (C, n = 27) were observed at farrowing. At delivery, the umbilical cord of each piglet was double tagged with identically numbered mouse ear tags to allow the piglet's weight to be matched to the corresponding placental weight. Litter size, placental weight, birth weight, and placental vascularity were recorded. Litter size was higher (12.0 +/- 0.7 vs 7.9 +/- 0.7) in S than in C (P < 0.001). Line differences in placental vascularity were not significant with or without adjustment for litter size (P = 0.45 and 0.39, respectively). Correlated response to selection for components of litter size resulted in a reduced birth weight (S 82.6% of C, P < 0.001) and a reduced placental weight (S 90.9% of C, P = 0.11). After adjusting for litter size, line differences in neither placental weight nor birth weight were significant (P = 0.40 and 0.07, respectively), which indicates that the reduction in birth weight was, for the most part, due to the increase in litter size. The result of the difference in the magnitude of the change for both weights was that placental efficiency, measured as the ratio of birth weight:placental weight was 0.43 higher in C (P = 0.05). Adjustment for litter size increased the difference in placental efficiency to 0.52 (P = 0.02). Since a significant difference in litter size favoring the selected line was observed, we hypothesize that this physiological response was achieved through mechanisms other than improved placental efficiency.

Components of growth in mice hemizygous for a MT/bGH transgene.

The objective of this study was to determine the effects of a metallothionein/bovine GH transgene on duration and rate of growth of lean and fat in mice. Mice were produced by mating hemizygous transgenic males to nontransgenic females. Ten weights and six measurements of total body electrical conductivity to estimate body composition were taken on 147 progeny between birth and 84 d of age. Growth traits for fat-free mass (FFM) and body fat mass (FM) were obtained by fitting FFM and FM to a logistic curve y = A/(1 + exp(k(b - t))), where y is FFM or FM, A is asymptotic mass, k and b are curve parameters, and t is time in days. The function and its first, second, and third derivatives for FFM and FM were used to model growth. A mixed model was used with animal and litter as random effects and trans-genotype, sex, and transgenotype x sex as fixed effects in analyses of growth traits. Estimates of transgeno-type and transgenotype x sex interaction were tested by using their corresponding standard errors. Males had greater response to the transgene than females in final FFM and growth rate during the entire growth period. Transgenic males and females had greater duration of lean growth than nontransgenics. Transgenic males began to accumulate fat later, but they eventually gained more fat than transgenic females.

Relationships of serum insulin-like growth factor I concentrations to growth, composition, and reproductive traits of swine.

Insulin-like growth factor I (IGF-I) is a peptide hormone that has been shown to be involved in metabolic regulation of growth and reproduction in livestock species. The objectives of this study were to quantify concentrations of IGF-I in growing pigs and determine whether IGF-I concentration can be used as a predictor of growth, composition, and reproductive traits. Forty male and 60 female pigs, divided equally between two locations, were weighed and bled at 3-wk intervals from 6 to 21 wk of age. At each sampling, two blood samples were collected via jugular venipuncture at an interval of at least 1 h. Serum was separated and IGF-I concentration determined via RIA. Pigs were weighed at each sampling date. Backfat and longissimus muscle area were measured with the use of B-mode ultrasound and adjusted to 100 kg. Age at puberty and first-parity litter size were measured on gilts. Effects of age, sex, location, and pig within sex x location on log-transformed IGF-I concentrations were determined by analyzing data as a split-plot. Performance traits were fitted to a model including the effects of IGF-I concentration, sex, location, and interactions. The IGF-I concentrations increased (P < .05) from 3 to 18 wk of age before dropping at 21 wk of age. Concentrations increased more rapidly in males than in females and differed significantly between sexes from 12 to 21 wk of age. Repeatability of IGF-I concentration was .29 +/- .02; IGF-I concentrations of samples collected at 6 wk were not correlated with those at later ages. Correlations between IGF-I concentrations of samples at later ages ranged from .27 to .51. Heritability of IGF-I concentration was .27 +/- .07. There was a tendency for weight to be affected by a sex x age interaction (P = .09). Weight of boars exceeded weight of gilts only at 21 wk (111.4 +/- 1.1 vs 107.1 +/- .8 kg). Regressions of weight on IGF-I concentrations were positive at all ages but greatest at 6 wk. The IGF-I concentration did not affect backfat thickness, longissimus area, percentage of lean, age at puberty, or litter size.

Effects of a controlled heat stress during late gestation, lactation, and after weaning on thermoregulation, metabolism, and reproduction of primiparous sows.

Heat stress (HS) causes seasonal infertility in sows and decreases reproductive efficiency. The objective was to examine thermoregulation, metabolic responses, and reproduction in sows exposed to HS or thermoneutral (TN) conditions during different phases of a production cycle (gestation, lactation, and breeding). Fifty-eight first-parity Landrace (n = 26) or Landrace × Large White F1 (n = 32) sows were rotated through environmental chambers for 57 d beginning in late gestation. The ambient temperature sequences included either TN (18°C to 20°C) or HS (24°C to 30°C) for each production phase with the following treatment groups: TN-TN-TN (n = 15), TN-HS-TN (n = 14), HS-TN-HS (n = 14), and HS-HS-HS (n = 15) for gestation-farrowing-breeding (20, 24, and 13 d, respectively). Regardless of the temperature treatment, rectal temperatures were greater (P < 0.001) during lactation (39.36°C ± 0.01°C) than during the gestation (38.27°C ± 0.01°C) or the breeding period (38.77°C ± 0.01°C). The increase in rectal temperature (P < 0.001) and respiration rate (P < 0.001) in response to the HS was greatest during lactation. There was an effect of day (P < 0.001) on serum IGF-1 and insulin concentrations because both insulin and IGF-1 increased after farrowing. Compared with HS sows, the TN sows had greater feed intake (P < 0.001) and greater serum concentrations of insulin (early lactation; P < 0.05) and IGF-1 (late lactation; P < 0.05) when they were lactating. The effects of HS on sow BW, back fat, and loin eye area were generally not significant. Average BW of individual piglets at weaning was approximately 0.5 kg lighter for the sows in the HS farrowing room (P < 0.05). Weaning-to-estrus interval, percentage sows inseminated after weaning, subsequent farrowing rate, and subsequent total born were not affected by treatment. In summary, regardless of ambient temperature, sows undergo pronounced and sustained changes in rectal temperature when they transition through gestation, lactation, weaning, and rebreeding. The effects of HS on rectal temperature, respiration rate, feed intake, and metabolic hormones were greatest during lactation. The controlled HS that we imposed affected piglet weaning weight, but rebreeding and subsequent farrowing performance were not affected.

An analysis of survey data by size of the breeding herd for the reproductive management practices of North American sow farms.

A survey was performed to assess whether reproductive management differed among small-sized (Sm, <500 sows), medium-sized (M, 501 to 2,000 sows), and large-sized (Lg, 2,001 to 8,000 sows) farms (n=113). Farms with 501 to 4000 sows/barn were most frequent with sows kept in stalls on 90% of farms. More Lg farms (P<0.05) functioned as breed to wean and more Sm and M as farrow to finish. More Sm and Lg farms weaned at >21 d, whereas M farms were more likely to wean at 18 to 21 d (P<0.05). More Lg farms had farrowing rates above 89% than Sm and M farms (P<0.05), and culling rates above 40% were more frequent on M and Lg farms than on S. On M and Lg farms, sows were bred in larger batches, using lower person to sow ratios, and with more people required than on Sm farms (P<0.05). More (P<0.05) M and Lg farms spent time moving sows and on records, but hours devoted to estrous detection, breeding, and other tasks did not differ among farms (P>0.10). More M and Lg farms used more boars for estrus detection, rotated boars, and controlled boar movement than Sm farms (P<0.05). Farm size also influenced semen sourcing, number of doses received, and frequency of semen delivery (P<0.05). More M and Lg farms performed AI in the presence of a boar, left the AI rod in after AI, checked for returns, and diagnosed pregnancy than Sm farms (P<0.05). Start of boar exposure after weaning began on 69% of farms within 2 d, occurring most often in the AM, but with exposure times varying from 1 to 5 min/sow. Semen was thermally protected for 50% of farms receiving shipments, and semen storage was consistent among farms. For AI, service occurred within minutes to hours after detection of estrus on 61% of farms. During AI, procedures such as back-pressure were required, whereas techniques such as hands-free AI were prohibited on most farms. Sow movement was allowed only once at 4 wk after breeding on 50% of farms, and pregnancy diagnosis occurred at 3 to 5 wk on 78% of farms. Most sows were allowed ≥1 chance for breeding after conception failure before culling. Incidence of fail to farrow was <5% and litter size was 10 to 13 pigs on >82% of farms. Summer infertility was observed on 69% of farms with estrus and pregnancy failures the leading causes. Over 70% of farms reported a technician effect on fertility. These results suggest that reproductive management of farms in key areas related to weaning, breeding, gestation, and labor use could be a source of variation in reproductive performance.

Selection for placental efficiency in swine: conceptus development.

The objective of this study was to evaluate correlated responses in conceptus development and traits physiologically relevant for placental function in swine from a selection experiment that resulted in differences in placental weight (PW) and efficiency (PE = birthweight/placental weight). Generation 3, second parity females from 2 lines with a history of selection on an index predicting either high PE (HPE) or low PE (LPE) were mated within line to produce Generation 4 litters for evaluation at d 30, 50, 70, 90, and 110 of gestation (n = 5/line × d combination). Maternal and fetal traits were analyzed by using a model including the fixed effects of line and gestational age, and the random effect of sire within line. Uterine length was not different between lines at any gestational age, but increased (P = 0.06) from 275.0 ± 23.1 cm at d 30 to 338.3 ± 23.3 cm at d 50, and remained relatively unchanged to d 110. Fetal weight was not different between lines from d 30 to 90, but was less (P = 0.02) in HPE than LPE at d 110 (1,280.6 ± 77.0 vs. 1,551.1 ± 75.3 g, respectively). Crown-rump length was not different between lines from d 30 to 70, but tended (P = 0.09) to be longer in HPE than LPE at d 90 (265.8 ± 8.8 vs. 241.2 ± 10.6 mm, respectively) and was shorter (P = 0.04) in HPE than LPE at d 110 (290.6 ± 5.0 vs. 304.9 ± 4.5 mm, respectively). Placental weight increased in both lines from d 30 to 50, at which point it remained relatively unchanged through the rest of pregnancy, except in LPE that showed a second increase from d 90 to 110. As a result, placental weight was not different between lines from d 30 to 90, but was less (P < 0.01) in HPE than LPE at d 110 (244.6 ± 32.3 vs. 379.2 ± 24.5 g, respectively). Line differences in placental efficiency were not significant at any gestational age. Implantation site length increased slowly for both lines from d 30 to 90, where it remained unchanged to d 110. Implantation site area was greater (P < 0.05) in HPE than LPE at d 30 and 50, but was not different between lines for the remainder of pregnancy. These results suggest that in Western breeds, a reduction in placental weight through selection is not accompanied by compensation in placental nutrient transfer and may result in decreased prenatal survival.