Date Full Report Received


Date Abstract Report Received



Primary Investigator:

Heat stress results in reduced feed intake, growth rate and reproductive performance, and most research has been aimed at these direct responses. It has also been shown that heat stress can reduce birth weight and increase number of stillborn piglets. Light birth weight pigs have smaller muscle fibers and adipocytes leading to less tender products, affecting the amount of marbling. Subsequent reproductive performance of piglets developing under heat stress conditions has not been reported and may magnify the true impact heat stress has on the U.S. swine industry.
This project was designed to collect data on economically important traits of growth, body composition, carcass quality, fat quality, puberty and subsequent reproductive performance on piglets developing in utero under heat stress (GTN) or thermoneutral (GTN) conditions.
Parity 1 females were artificially inseminated and housed under thermoneutral (GTN; 64.5-71.5ºF) or heat stress (GHS; 82.5-93ºF) daily temperature cycles throughout gestation, then lactated ~21d under TN conditions. At weaning, GHS and GTN gilts were housed together in pens of 22-25 gilts per pen. Barrows were double stocked here until approximately 55lbs (25kg), then 80 barrows were individually housed and fed in attempt to correct impact of in utero heat stress: a corn soybean meal diet that met (100%) or exceeded (110%) NRC lysine requirements; in the last 30 days barrows received a diet with 0 (CTL) or 7.4 ppm Paylean (PAY) until 266 lb (121kg). Weight, average daily gain (ADG), and feed disappearance (FD) were recorded. Week one weight was greater (P=0.03) in HS barrows (2183.00 ± 60.48 vs 1999.01 ± 59.66 g) but tended to be reduced (P=0.08) in HS barrows in late finishing (121.58±1.47 vs 125.26 ± 1.49 kg). In both grower (P=0.04) and finisher (P=0.05) phases, FD was greater in HS barrows (2.22 ± 0.05 vs 2.08 ± 0.05; 3.29 ± 0.08 vs 3.00 ± 0.08, respectively). PAY barrows had reduced (P<0.0001) ADG (0.96 ± 0.04 vs 0.75 ± 0.04 kg/d). In later finishing phases GHS pigs had greater LEA ( p=”0.03;” 40.13 ± 0.66 vs 38.15 ± 0.65 cm2); and PAY increased LEA at slaughter (54.89 ± 1.06 vs 48.85 ± 1.04 cm2). Carcass quality measures were recorded, and a chop was used to determine pork quality. PAY increased hot carcass weight (100.24 ± 1.19 vs 99.36 ± 1.18 kg, p=”0.02);” LEA (54.89 ± 1.05 vs 48.85 ± 1.04 cm2, P<0.01); and pH (5.62 ± 0.02 vs 5.56 ± 0.01, p=”0.01).” PAY 110% barrows had reduced 10th rib backfat ( p=”0.04)” compared to CTL 110% barrows (20.16 ± 1.26 vs 23.94 ± 1.23). 110% PAY barrows had greater %LEAN compared to 100% CTL, 110% CTL, and 100% PAY barrows (54.61 ± 0.71 vs 52.16 ± 0.69, 51.48 ±0.69, and 52.51 ± 0.69 %, P<0.05). At slaughter, samples were collected from the longissimus dorsi (LD) and semitendonosus (ST) for ATPase assay. The number and size of primary and secondary muscle fibers were determined. GHS increased secondary fibers in LD (58.17±1.17 vs 60.90±1.06 µm; p=”0.09)” and ST (67.70±1.36 vs 72.74±1.40 µm; p=”0.01).” GHS interactions with PAY were also found. Heat stress during gestation altered muscle development, resulting in increased muscle fiber size at harvest and a tougher product. Rectal, ear, and rump temperatures and respiration rate (RR) were recorded twice weekly from 3 to 6 months of age for gilts ( n=”165).” Room temperature ranged over time and time of day from 23.01°C-29.78°C (73.4-85.6°F). GHS pigs maintained body temperature with less effort, having lower RR (15.04±0.13 vs 15.83±0.15 breaths per min for GHS and GTN, respectively, P<0.001). Higher room temperatures at the time of measurement were associated with increased RR (12.28±0.49-19.62±0.49 breaths per min; P<0.001), though this did not differ by treatment. Gilts aged 193-198d were transported to Virginia Tech (TAREC). Estrus was recorded and synchronized to facilitate 68 litters born in four farrowing groups. GHS gilts tended to eat more during lactation (5.42±0.115 vs 5.12±0.114 kg/d; p=”.07)” with no effect on lactation weight loss. Numbers born, born alive or stillborn did not differ significantly by treatment, though numerically all favored GTN gilts (12.06±0.72 vs 12.94±0.72; 11.32±0.67 vs 11.76±0.67; 0.53±0.15 vs 0.47±0.15 for GHS vs GTN, respectively). GHS gilts tended to have lower piglet survival than GTN gilts (88.9±.02% vs 93.9±.02%; p=”.08).” A numerical non-significant difference of almost one piglet was observed favoring GTN gilts for total piglets weaned per litter (9.91±0.53 vs 10.85±0.53). The impact of heat stress on the swine industry has likely been underestimated using data on animals subjected to ambient temperatures outside of their thermoneutral zone. Preliminary data and data from other species suggest in utero environment could indeed have a significant effect on subsequent performance. This concept has not received due consideration, and in terms of thermal environment may help more accurately identify the value of cooling in gestation facilities. Being a fetus in a heat stressed dam appears to have negative impacts on feed efficiency and reproductive performance.
Key Findings:
• Differences between GHS and GTN piglets were not as large in this replicate as had been observed in previous replicates for body composition and temperature
• Differences did still exist, with GHS pigs eating more feed but not differing in weight gain or body composition.
• GHS pigs appear to be more active and spend more time at the feeder.
• While relatively small number of females were mated, reproductive differences between GHS and GTN gilts were largely non-significant but all favored the GHS gilts.
Dr. Tim Safranski
University of Missouri
(573) 884-7994