The annual replacement rate of commercial sows is 40 to 60% and for U.S. pork producers to remain globally competitive, research and technological advances are needed to increase sow lifetime productivity. Stress caused by inadequate floor space during the grow-finish phase of production has been shown to negatively impact some aspects of future reproduction in gilts. The effects of stress due to crowding in the nursery, when young pigs are perhaps more “fragile”, on future reproductive capacity in gilts, however, have not been adequately researched. Thus, the objectives of this project were: 1) to determine the effects of nursery space allocation on subsequent reproductive performance of gilts over three parities, and 2) to identify changes in performance, physiology, health, and immunology caused by crowding in the nursery that may provide insight into alterations in subsequent reproduction and sow longevity.
The experiment was conducted at a multiplication farm located in Cameron, NC that was owned and operated by Murphy-Brown LLC (Rose Hill, NC). A total of 2,537 maternal-line gilts (~22.3 days of age and ~12 pounds body weight) (Smithfield Premium Genetics, Rose Hill, NC) from 13 consecutive groups (weeks) of weaned pigs (~194.2 gilts/group) were utilized. After weaning, gilts were housed in an enclosed nursery barn in pens that each measured 5 x 5 ft. For each group of weaned pigs, pigs were assigned to one of three size classifications (small, medium, or large). Gilts from each size classification were then randomly assigned to space allowance treatments of 2.9, 2.0, or 1.6 ft2 /pig. Different floor space allowances were achieved by placing eight, eleven, or fourteen pigs per pen, respectively.
At the end of the nursery phase of production, gilts allowed the greatest amount of floor space weighed significantly more than gilts allowed the intermediate or least amount of floor space. Gilts allowed the greatest amount of floor space also had the greatest average daily gain.
A subset of 54 gilts from Group 5 was randomly selected evenly across treatments for blood collection on days 6 and 40. Blood was used for determination of serum cortisol concentrations, and complete blood counts and determination of the blood chemistry profile at the Virginia-Maryland Regional College of Veterinary Medicine. There was a significant interaction of treatment, size, and day on serum cortisol concentrations. For medium-sized gilts, females given the greatest and least, but not intermediate amount of floor space had increased cortisol concentrations from day 6 to day 40. Compared to medium-sized gilts given intermediate floor space, medium-sized gilts given the greatest amount of floor space had greater concentrations of cortisol on day 40. Small-sized gilts given the least amount of floor space had increased cortisol from day 6 to day 40.
There were many main and interactive effects of treatment, size and day on other blood response variables. For example, blood calcium was affected by treatment and was significantly greater for gilts given 2.9 or 2.0 ft2 of floor space than gilts allowed 1.6 ft2. Globulin tended to be affected by an interaction of treatment and day and increased from day 6 to 40 in gilts allowed 1.6 ft2 of floor space only. Creatine kinase and chloride were significantly affected by interactions of treatment and day. Creatine kinase increased with time in gilts allowed the greatest amount of floor space but not in gilts from the other two groups. Chloride increased with time for gilts allowed 2.9 or 2.0 ft2 of floor space but not in gilts allowed 1.6 ft2. Reticulocyte numbers tended to be affected by an interaction of treatment and day and on day 46 were greater in gilts allowed the greatest amount of floor space compared to the other two groups
On day 53 of the nursery phase of production, 30 gilts from Group 9 (10 gilts from each floor space allowance) were killed and the following weights and measures were recorded: BW, weights of the spleen, kidneys, liver, heart, uterus, and ovaries, vulva length, vulva width, and vulva area. The length and width of the vulva was also determined. There was a significant interaction of treatment and size on liver weight. Large gilts given the greatest amount of floor space had significantly greater liver weights than large gilts given either intermediate or the least amount of floor space. Medium gilts given the greatest amount of floor space tended to have greater liver weight than medium gilts given the intermediate amount of floor space. Within floor space allowances, medium-sized gilts given the greatest amount of floor space had greater liver weights than small gilts given the greatest amount of floor space.
In summary, restricted floor space allowances during the nursery phase of production reduced growth rate. There were inconsistent changes due to floor space allowance for concentrations of cortisol, the classical stress hormone which increases in response to acute stressors. There were, however, observed differences in blood constituents that are likely indicators of slight stress or reduced feed intake. Continuing study of the gilts from this experiment will determine the effects of floor space allowance in the nursery on subsequent sow performance and longevity. If the hypothesis of this study is substantiated (i.e., that crowding in the nursery negatively impacts future reproductive capacity), the benefits could be great in terms of pigs born and sow longevity. It is important that this avoidable type of production loss not be incurred. Moreover, if sows and gilts are culled due to reproductive performance that is actually a result of social stresses during the nursery phase of production rather than as a result of true genetic potential, then there is an inordinate cost for replacement females that can ultimately be avoided if this stress is understood and averted. Further, the genetic potential of these gilts may not, in fact, be realized simply because of a management “cap” inadvertently placed upon them early in life. This research will help with the development of overall best management practices for gilt development that increases lifetime productivity. Additionally, determining possible mechanisms whereby this loss occurs will provide fundamental information and ideas for additional research in swine focused on the effects of a variety of management practices and potential stresses experienced early-in-life on subsequent reproductive performance.