EFFECT OF PARITY ON THE REPRODUCTIVE PERFORMANCE OF NIGERIA INDIGENOUS SOWS AND THEIR PROGENY GROWTH PERFORMANCE DURING THE RAINY SEASON
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Abstract
The effects of parity of dam on the reproductive performance of Nigeria Indigenous (NI) sows and progeny growth performance in a commercial breeding farm in Enugu state, Nigeria was investigated in this study. One hundred (100) apparently healthy third trimester pregnant NI sows were randomly assigned to four (4) treatment groups in a completely randomized design (CRD) of twenty five (25) sows per group according to their reproductive parities as groups I, II, III and IV representing the first (P1), second (P2), third (P3) and fourth (P4) parities respectively. The mean litter size (LS) of P1 piglets (6.00±0.71 Head) was significantly (P < 0.05) lower when compared to the mean of P4 (8.50±0.65 Head) but showed no significant (P > 0.05) difference when compared to P2 (6.75±0.75 Head) and P3 (7.75±0.75 Head). The mean male LS was highest at P3 and lowest at P1 while there was a progressive increase in the mean female LS reaching top level at P4. The mean birth weight (BW) and mean male BW increased progressively from P1, reaching peak at P3 and then declined at P4 while the mean female BW reached peak at P2, declined at P3 and then increased at P4. The mean weaning weight (WW) and mean male WW were highest at P3 and lowest at P4 while the mean female WW was also highest at P3 (4.18±0.33 kg) but lowest at P1 (3.78±0.27 kg). The mean number of piglets weaned of P1 (5.25±0.63 Head) was significantly (P < 0.05) lower than P3 (7.00±0.41 Head), P4 (7.25±0.25 Head) but showed no significant (P > 0.05) reduction when compared to P2 (5.50±0.65 Head). The mean number of males weaned was highest at P3 and lowest at P2 which is similar to P4 while the mean number of females weaned was highest at P4 and lowest at P1. It can be concluded from this work that the reproductive performance of NI sows and its progeny growth performance were best at fourth parity (P4) of reproduction and the highest return on investment by swine breeders may be expected at this level of reproduction
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Bjorkman, S., Oliviero, C., Kauffold, J., Soede, N.M. and Peltoniemi, O.A.T. (2018c). Prolonged parturition and impaired placenta expulsion increase the risk of postpartum metritis and delay uterine involution in sows. Theriogenology, 106: 87-92.
Bjorkman, S., Oliviero, C., Rajala-Schultz, P.J., Soede, N.M. and Peltoniemi, O.A.T. (2017c). The effect of litter size, parity, farrowing duration on placenta expulsion and retention in sows. Theriogenology, 92: 36-44
Bloemhof, S., Vander Waaij, E.H., Merks, J.W.M. and Knol, E.F. (2008). Sow line differences in heat stress tolerance expressed in reproductive performance traits. Journal of Animal Science, 86: 3330–3337.
Carney-Hinkle, E.E., Tran, H., Bundy, J.W., Moreno, R., Miller, P.S. and Burkey, T.E. (2012). Effect of dam parity on litter performance, transfer of passive immunity, and progeny microbial ecology. Journal of Animal Science. (Accepted)
Clark, L.K., Leman, A.D. and Moris, R. (1988). Factors influencing litter size in swine: parity-one females. Journal of American Veterinary Medical Association, 192: 187-194.
Culbertson, M.S., Mabry, J.W., Bertrand, J.K. and Nelson, A. H. (1997). Breed specific adjustment factors for reproductive traits in Duroc, Hampshire, Landrace, and Yorkshire swine. Journal of Animal Science, 75: 2362-2367.
Damgaard, L.H., Rydhmer, L., Lovendahl, P. and Grandinson, K. (2003). Genetic parameters for within litter variation in piglet birth weight and change in within litter variation during suckling. Journal of Animal Science, 81: 604-610.
Dewey, C.E., Martin, S.W., Friendship, R.M. and Kennedy, B. (1992). A Delphi exercise used to identify potential causes of variation in litter size of Ontario swine. Canadian Veterinary Journal, 33: 40-45.
Engblom, L., Lundeheim, N., Dalin, A.M. and Andersson, K. (2007). Sow removal in Swedish commercial herds. Livestock Science, 106: 76–86.
FAO. (2014). Food security Indicators. FAO Statistics website (available at http://www.fao.org/economic/ess/ess-fs/ess-fadata/it/#.U4cSb3J-s1I)
Faust, M. A., Robison, O. W., and Tess, M. W. (1993). Genetic and economic analyses of sow replacement rates in the commercial tier of a hierarchical swine breeding structure. Journal of Animal Science, 71: 1400–1406
Gondret, F., Lefaucheur, L., Louveau, I., Lebret, B., Pichodo, X. and Le Cozler, Y. (2005). Influence of piglet birth weight on postnatal growth performance, tissue lipogenic capacity and muscle histological traits at market weight. Livestock Production Science, 93: 137-146.
Hagan, J. K. and Etim, N. N. (2019). The effects of breed, season and parity on the reproductive performance of pigs reared under hot and humid environments. Tropical Animal Health and Production, 51: 411-418.
Henchion, M., McCarthy, M., Resconi, V.C. and Troy, D. (2014). Meat consumption: Trends and quality matters. Meat Science, 98(3): 561-568.
Hoving, L.L., Soede, N.M., Feitsma H., Kemp B. (2012). Embryo survival, progesterone profiles and metabolic responses to an increased feeding level during second gestation in sows. Theriogenology, 77: 1557–1569.
Hoving, L.L., Soede, N.M., Graat, E.A.M., Feitsma, H. and Kemp, B. (2011). Reproductive performance of second parity sows: Relations with subsequent reproduction. Livestock Science, 140: 124–130.
Huang, Y.H., Yang, T.S., Lee, Y.P., Roan, S.W. and Liu, S.H. (2003). Effects of sire breed on the subsequent reproductive performances of Landrace sows. Asian-australAsian Journal of Animal Sciences, 16(4): 489–493.
Hughes, P. and Varley, M.A. (2003). Life time performance of the sow, In:Wiseman, J, Varley, MA, Kemp, B. (Eds.), Perspectives in Pig Science, Nottingham University Press, Notthingham, pp. 333-355.
Jian, Ye., Cheng, Tan., Xiaoxiang, Hu., Aiguo, Wang. and Zhenfang, Wu. (2018). Genetic parameters for reproductive traits at different parities in Large White pigs. Journal of Animal Science, 96(4): 1215–1220.
Kaiser, M., Jacobsen, S., Haubro-Andersen, P., Baekbo, P., Cerón, J., Dahl, J., Escribano, D. and Jacobson, M. (2018a). Inflammatory markers before and after farrowing in healthy sows and in sows affected with postpartum dysgalactia syndrome. BMC Veterinary Research, 14:83. Doi.org/10.1186/s12917-018-1382-7.
Kaiser, M., Jacobsen, S., Haubro-Andersen, P., Baekbo, P., Cerón, J., Dahl, J., Escribano, D., Theil, P. and Jacobson, M. (2018b). Hormonal and metabolic indicators before and after farrowing in sows affected with postpartum dysgalactia syndrome. BMC Veterinary Research, 14:334.Doi.org/10.1186/s12917-018-1649-z.
Keating, B.A., Herrero, M., Carberry, P.S., Gardner, J. and Cole, M.B. (2014). Food wedges: Framing the global food demand and supply towards 2050. Global Food Security-Agriculture Policy Economics and Environment, 3(3-4):125-132.
Knecht, D., Srodon, S. and Duzinski, K. (2015). The impact of season, parity and breed on selected reproductive performance parameters of sows. Archives of Animal Breeding, 58: 49–56.
Koketsu, Y. and Dial, G.D. (1997). Quantitative relationships between reproductive performance in sows and its risk factors. Pig News Information, 18: 47-52.
Koketsu, Y., Dial, G.D. and King, V.L. (1997). Returns to Service After Mating and Removal of Sows For Reproductive Reasons From Commercial Swine Farms. Theriogenology, 47(7): 1347-1363.
Koketsu, Y., Takahashi, H. and Akachi, K. (1999). Longevity, lifetime pig production and productivity, and age at first conception in a cohort of gilts observed over six years on commercial farms. Journal of Veterinary Medical Science, 61: 1001-1005.
Lucia Jr. T., Correa, M.N., Deschamps, J.C., Bianchi, I., Donin, M.A. and Machado, A.C. (2002). Risk factors for stillbirths in two swine farms in the south of Brazil. Preventive Veterinary Medicine, 53: 285–292.
Lucia, T., Dial, G.D. and Marsh, W.E. (1999). Estimation of Lifetime Productivity of Female Swine. Journal of American Veterinary Medical Association, 214(7): 1056-1059.
Mahan, D. C. (1998). Relationship of gestation protein and feed intake level over a five parity period using a high producing sow genotype. Journal of Animal Science, 76: 533-541.
Martineau, G.P., Farmer, C. and Peltoniemi, O.A.T. (2012). Mammary system. In: Diseases of swine (10th edition). Zimmerman JJ, Locke A, Karriker AR, Ramirez A, Schwartz KJ, Stevenson GW (Ed). John Wiley & Sons, Inc. Wiley-Blackwell, Ames, Iowa, USA, pp. 270-293.
MoFA. (2012). Agriculture in Ghana, Facts and Figures. Statistical, Research and Information Directorate, Ministry of Food and Agriculture, Ghana
Mote, B.E., Mabry, J.W., Stalder, K.J. and Rothschild, M.F. (2009). Evaluation of Current Reasons For Removal Of Sows From Commercial Farms. Professional Animal Scientist, 25(1): 1-7.
Mungate, F., Dzama, K., Mandisodza, K. and Shoniwa, A. (1999). Some non-genetic factors affecting commercial pig production in Zimbabwe. South African Journal of Animal Science, 29: 164–173.
Ncube, M., Dzama, K., Chimoyo, M., Kanengoni, A. and Hamdikuwanda, H. (2003). Effect of boar genotype on reproductive performance of the local sows of Zimbabwe. Livestock Research for Rural Development, 15(2): 1-11.
Oliviero, C. (2019). Factors affecting sow colostrum yield and composition, and their impact on piglet growth and health. Livestock Science. In press.
Oliviero, C., Junnikkala, S. and Peltoniemi, O.A.T. (2019). The challenge of large litters on the immune system of the sow and the piglets. Reproduction in Domestic Animals. In press
Oliviero, C., Kothe, S., Heinonen, M., Valros, A. and Peltoniemi, O. (2013). Prolonged duration of farrowing is associated with subsequent decreased fertility in sows. Theriogenology, 79(7): 1095-1099.
Patterson, J. L., Beltranena, E. and Foxcroft, G. R. (2010). The effect of gilt age at first estrus and breeding on third estrus on sow body weight changes and long-term reproductive performance. Journal of Animal Science, 88: 2500–2513.
Peltoniemi, O.A.T., Bjorkman, S. and Oliviero, C. (2016). Parturition effects on reproductive health in the gilt and sow. Reproduction in Domestic Animals, 51: 36-47
Quesnel, H., Brossard, L., Valancogne, A. and Quiniou, N. (2008). Influence of some sow characteristics on within litter variation of piglet birth weight. Animal, 2: 1842–1849.
Quiniou, N., Dagorn, J. and Gaudre, D. (2002). Variation of piglet’s birth weight and consequence on subsequent performance. Livestock Production Science, 78: 63-70.
Rekwot, P.I., Jegede, J.O., Ehoche, O.W. and Tegbe, T.S.B. (2001). Reproductive performance in small holder piggeries in northern Nigeria. Trop Agric (Trinidad); 78: 1–4.
Scholman, G. J. and Dijkhuizen, A. A. (1989). Determination and analysis of the economic optimum culling strategy in swine breeding herds in Western Europe and the USA, Neth. Journal of Agricultural Science, 37: 71–74.
Serenius, T. and Stalder, K.J. (2006). Selection for sow longevity. Journal of Animal Science, 84: 166-171.
Stalder, K.J., Knauer, M., Baas, T.J., Rothschild, M.F. and Mabry, J.W. (2004). Sow Longevity. Pig News and Information, 25(2): 53-74.
Stalder, K.J., Lacy, R.C., Cross, T.L. and Conatser, G.E. (2003). Financial Impact Of Average Parity Of Culled Females In A Breed-To-Wean Swine Operation Using Replacement Gilt Net Present Value Analysis. Journal of Swine Health and Production, 11(2): 69-74.
Steel, R. G. D. and Torrie, J. H. (1980). Principles and procedures of statistics, Second Edition, New York: McGraw-Hill Book Co.
Suriyasomboon, A., Lundeheim, N., Kunavonkrit, A. and Einarsson, S. (2006). Effect of temperature and humidity on reproductive performance of crossbred sows in Thailand. Theriogenology, 65: 606–628.
Svoboda, M. and Drabek, J. (2005). Iron deficiency in suckling piglets: Parenteral and oral iron administration to piglets. Folia Vet.; 49(3):165-174.
Takai, Y. and Koketsu, Y. (2008). Number of services and the re-service intervals in relation to suboptimal reproductive performance in female pigs on commercial farms. Livestock Science, 114: 42–47.
Tummaruk, P., Lundeheim, N., Einarsson, S. and Dalin, A.M. (2000). Reproductive performance of purebred Swedish Landrace and Swedish Yorkshire sows: I. Seasonal variation and parity influence. Acta Agriculturae Scandinavica Section A - Animal Science, 50: 205-216.
Tummaruk, P., Tantasuparuk, W., Techakumphu, M. and Kunavongkrit, A. (2010). Seasonal influences on the litter size at birth of pigs are more pronounced in the gilt than sow litters. Journal of Agricultural Science, 148: 421–432.
United Nations. (2013). National Transfer Accounts Manual: Measuring and Analysing the Generational Economy. Sales No. E.13.XIII.6. Available from http://www.un.org/ en/development/desa/publications/measuring-and-analysing-the-generational-economy.html.
Van Dijk, A.J., Van Rens, B.T.T.M., Van Der Lende, T. and Taverne, M.A.M. (2005). Factors affecting duration of the expulsive stage of parturition and piglet birth intervals in sows with uncomplicated, spontaneous farrowings. Theriogenology, 64: 1573–1590.
Wilson, E. R. and Johnson, R. K. (1980). Adjustment of 21 day litter weight for number of pigs nursed for purebred and crossbred dams. Journal of Animal Science, 51: 37-42.
Wood, C.M., Christian, L.L. and Rothschild, M.F. (1990). Factors to adjust litter weight of pigs to a standard 21 days of age. Journal of Animal Science, 68: 2628-2633.
Xue, J.L., Dial, G.D., Marsh, W.E., Davies, P.R. and Lucia, T. (1997). Association between lactation length and sow reproductive performance and longevity. Journal of American Veterinary Medical Association, 210: 935-938.
Yilma, T. (2017). Study on reproductive performance of breeding sows and ultrasound monitoring of ovarian follicle activity and ovulation of post-weaning sows in a commercial pig farm of central Ethiopia. Vet. Med. Open J.., 2(3): 76–82.
Bjorkman, S., Oliviero, C., Kauffold, J., Soede, N.M. and Peltoniemi, O.A.T. (2018c). Prolonged parturition and impaired placenta expulsion increase the risk of postpartum metritis and delay uterine involution in sows. Theriogenology, 106: 87-92.
Bjorkman, S., Oliviero, C., Rajala-Schultz, P.J., Soede, N.M. and Peltoniemi, O.A.T. (2017c). The effect of litter size, parity, farrowing duration on placenta expulsion and retention in sows. Theriogenology, 92: 36-44
Bloemhof, S., Vander Waaij, E.H., Merks, J.W.M. and Knol, E.F. (2008). Sow line differences in heat stress tolerance expressed in reproductive performance traits. Journal of Animal Science, 86: 3330–3337.
Carney-Hinkle, E.E., Tran, H., Bundy, J.W., Moreno, R., Miller, P.S. and Burkey, T.E. (2012). Effect of dam parity on litter performance, transfer of passive immunity, and progeny microbial ecology. Journal of Animal Science. (Accepted)
Clark, L.K., Leman, A.D. and Moris, R. (1988). Factors influencing litter size in swine: parity-one females. Journal of American Veterinary Medical Association, 192: 187-194.
Culbertson, M.S., Mabry, J.W., Bertrand, J.K. and Nelson, A. H. (1997). Breed specific adjustment factors for reproductive traits in Duroc, Hampshire, Landrace, and Yorkshire swine. Journal of Animal Science, 75: 2362-2367.
Damgaard, L.H., Rydhmer, L., Lovendahl, P. and Grandinson, K. (2003). Genetic parameters for within litter variation in piglet birth weight and change in within litter variation during suckling. Journal of Animal Science, 81: 604-610.
Dewey, C.E., Martin, S.W., Friendship, R.M. and Kennedy, B. (1992). A Delphi exercise used to identify potential causes of variation in litter size of Ontario swine. Canadian Veterinary Journal, 33: 40-45.
Engblom, L., Lundeheim, N., Dalin, A.M. and Andersson, K. (2007). Sow removal in Swedish commercial herds. Livestock Science, 106: 76–86.
FAO. (2014). Food security Indicators. FAO Statistics website (available at http://www.fao.org/economic/ess/ess-fs/ess-fadata/it/#.U4cSb3J-s1I)
Faust, M. A., Robison, O. W., and Tess, M. W. (1993). Genetic and economic analyses of sow replacement rates in the commercial tier of a hierarchical swine breeding structure. Journal of Animal Science, 71: 1400–1406
Gondret, F., Lefaucheur, L., Louveau, I., Lebret, B., Pichodo, X. and Le Cozler, Y. (2005). Influence of piglet birth weight on postnatal growth performance, tissue lipogenic capacity and muscle histological traits at market weight. Livestock Production Science, 93: 137-146.
Hagan, J. K. and Etim, N. N. (2019). The effects of breed, season and parity on the reproductive performance of pigs reared under hot and humid environments. Tropical Animal Health and Production, 51: 411-418.
Henchion, M., McCarthy, M., Resconi, V.C. and Troy, D. (2014). Meat consumption: Trends and quality matters. Meat Science, 98(3): 561-568.
Hoving, L.L., Soede, N.M., Feitsma H., Kemp B. (2012). Embryo survival, progesterone profiles and metabolic responses to an increased feeding level during second gestation in sows. Theriogenology, 77: 1557–1569.
Hoving, L.L., Soede, N.M., Graat, E.A.M., Feitsma, H. and Kemp, B. (2011). Reproductive performance of second parity sows: Relations with subsequent reproduction. Livestock Science, 140: 124–130.
Huang, Y.H., Yang, T.S., Lee, Y.P., Roan, S.W. and Liu, S.H. (2003). Effects of sire breed on the subsequent reproductive performances of Landrace sows. Asian-australAsian Journal of Animal Sciences, 16(4): 489–493.
Hughes, P. and Varley, M.A. (2003). Life time performance of the sow, In:Wiseman, J, Varley, MA, Kemp, B. (Eds.), Perspectives in Pig Science, Nottingham University Press, Notthingham, pp. 333-355.
Jian, Ye., Cheng, Tan., Xiaoxiang, Hu., Aiguo, Wang. and Zhenfang, Wu. (2018). Genetic parameters for reproductive traits at different parities in Large White pigs. Journal of Animal Science, 96(4): 1215–1220.
Kaiser, M., Jacobsen, S., Haubro-Andersen, P., Baekbo, P., Cerón, J., Dahl, J., Escribano, D. and Jacobson, M. (2018a). Inflammatory markers before and after farrowing in healthy sows and in sows affected with postpartum dysgalactia syndrome. BMC Veterinary Research, 14:83. Doi.org/10.1186/s12917-018-1382-7.
Kaiser, M., Jacobsen, S., Haubro-Andersen, P., Baekbo, P., Cerón, J., Dahl, J., Escribano, D., Theil, P. and Jacobson, M. (2018b). Hormonal and metabolic indicators before and after farrowing in sows affected with postpartum dysgalactia syndrome. BMC Veterinary Research, 14:334.Doi.org/10.1186/s12917-018-1649-z.
Keating, B.A., Herrero, M., Carberry, P.S., Gardner, J. and Cole, M.B. (2014). Food wedges: Framing the global food demand and supply towards 2050. Global Food Security-Agriculture Policy Economics and Environment, 3(3-4):125-132.
Knecht, D., Srodon, S. and Duzinski, K. (2015). The impact of season, parity and breed on selected reproductive performance parameters of sows. Archives of Animal Breeding, 58: 49–56.
Koketsu, Y. and Dial, G.D. (1997). Quantitative relationships between reproductive performance in sows and its risk factors. Pig News Information, 18: 47-52.
Koketsu, Y., Dial, G.D. and King, V.L. (1997). Returns to Service After Mating and Removal of Sows For Reproductive Reasons From Commercial Swine Farms. Theriogenology, 47(7): 1347-1363.
Koketsu, Y., Takahashi, H. and Akachi, K. (1999). Longevity, lifetime pig production and productivity, and age at first conception in a cohort of gilts observed over six years on commercial farms. Journal of Veterinary Medical Science, 61: 1001-1005.
Lucia Jr. T., Correa, M.N., Deschamps, J.C., Bianchi, I., Donin, M.A. and Machado, A.C. (2002). Risk factors for stillbirths in two swine farms in the south of Brazil. Preventive Veterinary Medicine, 53: 285–292.
Lucia, T., Dial, G.D. and Marsh, W.E. (1999). Estimation of Lifetime Productivity of Female Swine. Journal of American Veterinary Medical Association, 214(7): 1056-1059.
Mahan, D. C. (1998). Relationship of gestation protein and feed intake level over a five parity period using a high producing sow genotype. Journal of Animal Science, 76: 533-541.
Martineau, G.P., Farmer, C. and Peltoniemi, O.A.T. (2012). Mammary system. In: Diseases of swine (10th edition). Zimmerman JJ, Locke A, Karriker AR, Ramirez A, Schwartz KJ, Stevenson GW (Ed). John Wiley & Sons, Inc. Wiley-Blackwell, Ames, Iowa, USA, pp. 270-293.
MoFA. (2012). Agriculture in Ghana, Facts and Figures. Statistical, Research and Information Directorate, Ministry of Food and Agriculture, Ghana
Mote, B.E., Mabry, J.W., Stalder, K.J. and Rothschild, M.F. (2009). Evaluation of Current Reasons For Removal Of Sows From Commercial Farms. Professional Animal Scientist, 25(1): 1-7.
Mungate, F., Dzama, K., Mandisodza, K. and Shoniwa, A. (1999). Some non-genetic factors affecting commercial pig production in Zimbabwe. South African Journal of Animal Science, 29: 164–173.
Ncube, M., Dzama, K., Chimoyo, M., Kanengoni, A. and Hamdikuwanda, H. (2003). Effect of boar genotype on reproductive performance of the local sows of Zimbabwe. Livestock Research for Rural Development, 15(2): 1-11.
Oliviero, C. (2019). Factors affecting sow colostrum yield and composition, and their impact on piglet growth and health. Livestock Science. In press.
Oliviero, C., Junnikkala, S. and Peltoniemi, O.A.T. (2019). The challenge of large litters on the immune system of the sow and the piglets. Reproduction in Domestic Animals. In press
Oliviero, C., Kothe, S., Heinonen, M., Valros, A. and Peltoniemi, O. (2013). Prolonged duration of farrowing is associated with subsequent decreased fertility in sows. Theriogenology, 79(7): 1095-1099.
Patterson, J. L., Beltranena, E. and Foxcroft, G. R. (2010). The effect of gilt age at first estrus and breeding on third estrus on sow body weight changes and long-term reproductive performance. Journal of Animal Science, 88: 2500–2513.
Peltoniemi, O.A.T., Bjorkman, S. and Oliviero, C. (2016). Parturition effects on reproductive health in the gilt and sow. Reproduction in Domestic Animals, 51: 36-47
Quesnel, H., Brossard, L., Valancogne, A. and Quiniou, N. (2008). Influence of some sow characteristics on within litter variation of piglet birth weight. Animal, 2: 1842–1849.
Quiniou, N., Dagorn, J. and Gaudre, D. (2002). Variation of piglet’s birth weight and consequence on subsequent performance. Livestock Production Science, 78: 63-70.
Rekwot, P.I., Jegede, J.O., Ehoche, O.W. and Tegbe, T.S.B. (2001). Reproductive performance in small holder piggeries in northern Nigeria. Trop Agric (Trinidad); 78: 1–4.
Scholman, G. J. and Dijkhuizen, A. A. (1989). Determination and analysis of the economic optimum culling strategy in swine breeding herds in Western Europe and the USA, Neth. Journal of Agricultural Science, 37: 71–74.
Serenius, T. and Stalder, K.J. (2006). Selection for sow longevity. Journal of Animal Science, 84: 166-171.
Stalder, K.J., Knauer, M., Baas, T.J., Rothschild, M.F. and Mabry, J.W. (2004). Sow Longevity. Pig News and Information, 25(2): 53-74.
Stalder, K.J., Lacy, R.C., Cross, T.L. and Conatser, G.E. (2003). Financial Impact Of Average Parity Of Culled Females In A Breed-To-Wean Swine Operation Using Replacement Gilt Net Present Value Analysis. Journal of Swine Health and Production, 11(2): 69-74.
Steel, R. G. D. and Torrie, J. H. (1980). Principles and procedures of statistics, Second Edition, New York: McGraw-Hill Book Co.
Suriyasomboon, A., Lundeheim, N., Kunavonkrit, A. and Einarsson, S. (2006). Effect of temperature and humidity on reproductive performance of crossbred sows in Thailand. Theriogenology, 65: 606–628.
Svoboda, M. and Drabek, J. (2005). Iron deficiency in suckling piglets: Parenteral and oral iron administration to piglets. Folia Vet.; 49(3):165-174.
Takai, Y. and Koketsu, Y. (2008). Number of services and the re-service intervals in relation to suboptimal reproductive performance in female pigs on commercial farms. Livestock Science, 114: 42–47.
Tummaruk, P., Lundeheim, N., Einarsson, S. and Dalin, A.M. (2000). Reproductive performance of purebred Swedish Landrace and Swedish Yorkshire sows: I. Seasonal variation and parity influence. Acta Agriculturae Scandinavica Section A - Animal Science, 50: 205-216.
Tummaruk, P., Tantasuparuk, W., Techakumphu, M. and Kunavongkrit, A. (2010). Seasonal influences on the litter size at birth of pigs are more pronounced in the gilt than sow litters. Journal of Agricultural Science, 148: 421–432.
United Nations. (2013). National Transfer Accounts Manual: Measuring and Analysing the Generational Economy. Sales No. E.13.XIII.6. Available from http://www.un.org/ en/development/desa/publications/measuring-and-analysing-the-generational-economy.html.
Van Dijk, A.J., Van Rens, B.T.T.M., Van Der Lende, T. and Taverne, M.A.M. (2005). Factors affecting duration of the expulsive stage of parturition and piglet birth intervals in sows with uncomplicated, spontaneous farrowings. Theriogenology, 64: 1573–1590.
Wilson, E. R. and Johnson, R. K. (1980). Adjustment of 21 day litter weight for number of pigs nursed for purebred and crossbred dams. Journal of Animal Science, 51: 37-42.
Wood, C.M., Christian, L.L. and Rothschild, M.F. (1990). Factors to adjust litter weight of pigs to a standard 21 days of age. Journal of Animal Science, 68: 2628-2633.
Xue, J.L., Dial, G.D., Marsh, W.E., Davies, P.R. and Lucia, T. (1997). Association between lactation length and sow reproductive performance and longevity. Journal of American Veterinary Medical Association, 210: 935-938.
Yilma, T. (2017). Study on reproductive performance of breeding sows and ultrasound monitoring of ovarian follicle activity and ovulation of post-weaning sows in a commercial pig farm of central Ethiopia. Vet. Med. Open J.., 2(3): 76–82.