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A retrospective study on the preserving capacity of a commercial boar semen extender

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A retrospective study on the preserving capacity of a commercial boar semen extender
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  A retrospective study on the preserving capacityof a commercial boar semen extender Sukumarannair S. Anil a , Alejandro Larriestra a , John Deen a,* ,Robert B. Morrison a , Luke Minion b a  Department of Clinical and Population Sciences, College of Veterinary Medicine,University of Minnesota, 1988 Fitch Avenue, Saint Paul, MN 55108, USA b Pipestone Veterinary Clinic, Pipestone, MN, USA Received 12 March 2003; accepted 18 October 2003 Abstract Theobjective ofthisstudywas toevaluate the preservingcapacity ofacommercial, long-termboarsemen extender beyond 4 days in terms offarrowing failure and total born per litter in sows and gilts.Data from 21 farms were subjected to logistic and linear regression analyses to assess the effect of parity (2–5, >5 and gilts), wean-to-service interval (  5 and  6 days) and number of AI (1, 2, or 3) onthe association between semen age (  6, 7, 8, 9, and   10 days) and fertility. As the semen ageincreased, the likelihood offarrowing failure increased and total born per litter decreased in sows andgilts. The effect of semen ageing on farrowing failurewas more pronounced insows than in gilts as inthe latter it became significant only after 8 days. The effect of semen ageing on total born per litterwas similar inbothsowsandgilts.A lowerparityand wean-to-service intervalwere associated withareduction in farrowing failure and increase in total born per litter in sows. Increasing the number of inseminations up to two was beneficial in reducing farrowing failure in sows and gilts. A thirdinsemination increased the likelihood offarrowing failure in sows. The number of total born per litterin sows increased with number of inseminations and the effect was not significant in gilts. # 2003 Elsevier Inc. All rights reserved. Keywords:  Semen age; Extender; Fertility; Sow; Gilt 1. Introduction Thesuccess ofAIdependsontheextenttowhich semencanbepreservedwithoutlossof fertility. Fresh semen is perishable and the way to improve storage life of fresh semen is Theriogenology 62 (2004) 425–436 * Corresponding author. Tel.:  þ 1-612-625-7784; fax:  þ 1-612-625-1210. E-mail address:  deenx003@umn.edu (J. Deen).0093-691X/$ – see front matter # 2003 Elsevier Inc. All rights reserved.doi:10.1016/j.theriogenology.2003.10.019  dilution in an appropriate extender and storage at a constant cool temperature of 16 – 18  8 C[1]. The semen extender enables the semen to remain in a viable state for a variable periodwithout a loss in the fertilizing capacity of spermatozoa and enables AI with a minimumdose at minimal cost and health risk  [2].Commercial boar semen extenders vary in composition and are classi fi ed as short-term(<3 days) and long-term (>3 days) extenders based on how long they can preserve liquidsemenwithoutconsiderablelossinitsfertility.Thereductioninfertilityofstoredsemenisa gradual process (beginning at ejaculation), regardless of the use of the extender used.The boar, its breed, and the frequency of semen collection are critical in determiningfertility. The fertility of stored boar semen depends mainly on initial semen quality,numberofspermatozoaperinseminationandtypeofextender[3],semenstoragetimeandconditions, and interval between insemination and ovulation [4,5]. Number of insemina-tions [6], the interval between weaning to  fi rst service and parity of the female, alsoin fl uence fertility.A long-term extender is generally preferred to a short-term extender because the formerensures longer shelf life and thereby reduces the need for frequent semen delivery. This isof special relevance in countries, such as the USA, where swine farms are spread over widedistances. Reduction in the number of semen deliveries means a reduction in the likelihoodof a breach in biosecurity as well. Attempts are ongoing to develop extenders with longersemen preserving potential. Enduraguard TM is an extender developed by Minitube(Minitube of America, Verona, WI, USA), which is a modi fi cation of the long-termextender Androhep TM .A retrospective study of a boar stud was performed to analyze the fertility of boar semenextended in Enduraguard TM and stored for up to  10 days, in terms of farrowing failureand total born per litter in sows and gilts. The semen from this boar stud was released foruse only after 4 days after collection and laboratory analysis to ensure the semen was freefrom porcine reproductive and respiratory syndrome (PRRS) virus. The objective of thestudy therefore, was to assess the loss of fertility from 4 to   10 days. 2. Material and methods The study involved 35,300 parity records from 21 commercial farms in Minnesota,USA retrieved from PigCHAMP database (PigCHAMP Inc. Ames, IA, USA) fromJanuarytoOctober2002.ThesowsandgiltsbelongedtoPIC(PigImprovementCompany,USAInc.)linesandallwerestall-housed,withrestrictedfeeding(1.8 – 3.2 kg)duringpostweaning and gestation periods. All open sows and gilts were examined once daily forestrussignseachmorning.Allfemalesfoundinestruswereimmediatelyinseminatedandon the following mornings if the females were still in estrus. Sows and gilts wereinseminated once, twice or thrice during each estrus using mixed semen from an in-house PIC boar stud, extended in Enduraguard TM . Each dose of semen was labeled withthe date of collection and this information was recorded into the PigCHAMP database atthe time of AI. Data on the parity, wean-to-service interval, number ofinseminations, ageof the semen used, farrowing success/failure and total number of piglets born/litter werecollected for analysis. 426  S.S. Anil et al./Theriogenology 62 (2004) 425–436   The production outcomes evaluated were farrowing failure and total born per litter forsows and gilts. For the purpose of this analysis, the age of the semen used for sows andgilts that received at least one AI was categorized as  fi rst insemination semen age (1SA)and the age of the semen used for sows and gilts that received at least two inseminationswas categorized as second insemination semen age (2SA). The semen age at use wascategorized as   6 days (i.e., 5 and 6 days), 7 days, 8 days, 9 days, and   10 days. Theparity of sows was categorized as parity 2 to 5 and parity >5. The weaning to serviceinterval (WSI) for the sows was categorized as   5 days and   6 days. Separateregression models were  fi tted for  fi rst and second insemination semen ages as theywere correlated (Spearman  r  0.50 with  P < 0 : 01). Multi-variate logistic (Proc logistic)regression models were  fi tted to evaluate the effect of semen age on farrowing failurewith the number of AI per service, WSI and parity as the explanatory variables for sowsand the number of AI per service as the only explanatory variable for gilts. A likelihoodratio Chi-square test was used to evaluate the  fi t of the models. The same set of variableswas tested including farm as a random effect in the logistic mixed model (Glimmixmacro). Separate multi-variate linear regression models for sows and gilts were  fi tted toevaluate the effect of semen age on total born per litter with the same explanatoryvariables, including farm as a random effect (Proc Mixed). All statistical analyzes wereperformed using the statistical software package, SAS v. 8.2 2001 (SAS Institute, Cary,NC, USA). 3. Results The number of observations in each category of semen age for both sows and gilts ispresentedin Table 1.The distributionofobservations fordifferent semen ages forsows andgilts for both 1SA and 2SA categories were similar. The likelihood ratio Chi-square testindicated that neither age of semen nor number of inseminations was signi fi cantwith respect to the 2SA in gilts. However, the odds ratios of this model have also been Table 1Number of observations for first insemination semen age (semen age for  1 AI) and second-insemination semenage (semen age for   2 AI) for sows and gilts Semenage(day)Sows GiltsFirstinseminationsemen age(1SA)Percentage Secondinseminationsemen age(2SA)Percentage Firstinseminationsemen age(1SA)Percentage Secondinseminationsemen age(2SA)Percentage  6 9260 35.26 5998 27.27 3304 36.56 1955 32.447 7060 26.88 5952 27.06 1939 21.46 1296 21.518 4864 18.52 5740 26.09 1621 17.94 1273 21.13 9  2682 10.21 2590 11.77 1224 13.55 783 12.99  10 2398 9.13 1718 7.81 948 10.49 719 11.93Total 26264 100 21998 100 9036 100 6026 100 S.S. Anil et al./Theriogenology 62 (2004) 425  –  436   427  presented. Farm did not have signi fi cant effect in both the models for farrowing failure andlitter size. 3.1. Association of first (1SA) and second insemination semen age (2SA) categorieswith farrowing failure in sows The association of semen ages, parity, WSI and number of AI with farrowing failure insows are presented in Table 2. The likelihood of farrowing failure among sows increasedsigni fi cantly ( P < 0 : 001) with the age of the semen with the exception of 9 days( P < 0 : 01) and 7 days ( P > 0 : 05) old semen in the 2SA category. The proportion of farrowing failure associated with different semen ages shown in Fig. 1 also revealed thisassociation. The likelihood of farrowing failure was signi fi cantly ( P < 0 : 001) less forsows of parity 2 – 5 compared to sows of parity >5 in both 1SA and 2SA categories.Increasing the number of inseminations was found to be associated with a reduction inthe likelihood of farrowing failure with respect to  fi rst insemination semen age category;inseminating twice signi fi cantly ( P < 0 : 001) reduced the likelihood of farrowing failurewhen compared to inseminating once. Inseminating thrice did not reduce the likelihoodof farrowing failure in sows signi fi cantly in this semen age category. However, in the2SA category inseminating thrice signi fi cantly ( P < 0 : 001) increased the likelihood of farrowing failure. Table 2Odds ratios and confidence intervals for semen ages, parity, wean to service interval and number of AI frommulti-variate logistic regression model for the association of 1SA (semen age for  1 AI) and 2SA (semen agefor   2 AI) categories with farrowing failure in sowsEffect First insemination semen age(1SA)Second insemination semen age(2SA)Odds ratio Confidence limits Odds ratio ConfidencelimitsSemen age   10 days vs. semenage   6 days1.366 1.200 – 1.555 *** 1.623 1.396 – 1.887 *** Semen age 9 days vs. semenage   6 days1.377 1.217 – 1.558 *** 1.216 1.058 – 1.398 ** Semen age 8 days vs. semenage   6 days1.241 1.119 – 1.377 *** 1.327 1.188 – 1.482 *** Semen age 7 days vs. semenage   6 days1.201 1.093 – 1.320 *** 1.067 0.951 – 1.196 NS Parity 2 – 5 vs. parity > 5 0.695 0.620 – 0.779 *** 0.650 0.574 – 0.736 *** WSI  6 days vs. WSI  5 days 1.442 1.327 – 1.567 *** 1.492 1.355 – 1.643 *** 3 AI vs. 1 AI 0.979 0.865 – 1.108 NS NA NA2 AI vs. 1 AI 0.757 0.689 – 0.832 *** NA NA3 AI vs. 2 AI NA NA 1.300 1.175 – 1.439 *** NA: not applicable; NS: non-signi fi cant. ** P < 0 : 01. *** P < 0 : 001.428  S.S. Anil et al./Theriogenology 62 (2004) 425–436   3.2. Association of   fi rst (1SA) and second insemination semen age (2SA) categorieswith farrowing failure in gilts In both the 1SA and 2SA categories, the likelihood of farrowing failure among giltsincreased with the age of semen, with the exceptionof 7days old semen in 2SA categoryinwhich, the likelihood of farrowing failure decreased (Table 3). However, none of theseassociations except that of 9 days old semen in 1SA category was signi fi cant ( P < 0 : 001).This association is in linewith the proportion offarrowing failure associated with differentsemen ages (Fig. 2). Increasing the number of inseminations signi fi cantly reduced the Fig. 1. Proportion of farrowing failure in sows for 1SA (semen age for  1 AI) and 2SA (semen age for  2 AI)categories.Table 3Odds ratios, confidence intervals and  P  values for semen ages and number of AI from multi-variate logisticregression model for the association of 1SA (semen age for  1 AI) and 2SA (semen age for  2 AI) categorieswith farrowing failure in giltsEffect First insemination semen age(1SA)Second insemination semen age(2SA)Odds ratio Confidence limits Odds ratio Confidence limitsSemen age   10 days vs. semenage   6 days1.193 0.977 – 1.456 NS 1.065 0.822 – 1.380 NS Semen age 9 days vs. semenage   6 days1.456 1.222 – 1.736 *** 1.066 0.829 – 1.370 NS Semen age 8 days vs. semenage   6 days1.071 0.903 – 1.270 NS 1.021 0.822 – 1.267 NS Semen age 7 days vs. semenage   6 days1.019 0.865 – 1.200 NS 0.957 0.769 – 1.191 NS 3 AI vs. 1 AI 0.477 0.362 – 0.629 *** NA NA2 AI vs. 1 AI 0.536 0.475 – 0.605 *** NA NA3 AI vs. 2 AI NA NA 0.895 0.680 – 1.177 NS NA: not applicable; NS: non signi fi cant. *** P < 0 : 001. S.S. Anil et al./Theriogenology 62 (2004) 425  –  436   429
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