پديد آورندگان :
شهدادي، عليرضا دانشگاه فردوسي مشهد - گروه علوم دامي , شريعتي، محمدمهدي دانشگاه فردوسي مشهد - گروه علوم دامي , نصيري، محمدرضا دانشگاه فردوسي مشهد - گروه علوم دامي , زره داران، سعيد دانشگاه فردوسي مشهد - گروه علوم دامي , ساقي، داوودعلي مركز تحقيقات و آموزش كشاورزي و منابع طبيعي خراسان رضوي
چكيده لاتين :
Introduction: Reducing of economic lifetime and culling of cow are costly and sophisticatedly process in animal industries (Dohoo et al. 2010). In dairy cattle herds, productive and economic lifetime of cow is important because of their substantial effects on pure benefit of every dairy farm. The productive lifetime is called the interval between calving and culling of cow (Vollema and Groen 1996; Sewalem et al. 2005). Nowadays lifespan is considerably noticed because of increasing of rate culling dairy cattle in most of herds. High culling of dairy cows lead-in few cows get to physical maturity stage and complete production (McCullough and DeLorenzo 1996).
Recognizing of most important factors affecting culling of dairy cows, longevity performance and economical lifetime and survival distribution function can use for making appropriate breeding strategies in order to improving of longevity and productive lifetime of Iranian Holstein dairy cow. So, the objective of this study was to investigate the culling reasons and factors affecting it and to determine survival distribution function in Iranian Holstein dairy cows.
Material and methods: In This study, the records of lifespan and culling of 971428 Holstein dairy cows from 3872 herds during 1996 to 2013 were used. Data were collected by the Animal Breeding Center of Iran. Initial data were edited using R and FoxPro 2.6. In Iranian dairy cattle database, 55 reasons of culling were presented, so we categorized them to 12 general groups. For determination of frequencies of culling reasons, survival package of R program was used (Therneau 2015).
In this study, season, age at first calving, parity, lactation stage and milk yield as factors affecting culling (independent variables) were investigated. For analyzing of data logistic procedure of SAS 9.2 were used.
Lifetime of animals was evaluated as number of days from birth to culling or censoring of data. Cows that were not culled at the beginning of the study, as censored records considered and the zero code (0 censor code) was assigned to them. Also, culled animals that having culled code were considered as not censored (1 censor cod). In order to determine survival distribution function in Iranian Holstein dairy cow, lifetest procedure of SAS 9.2 were used. Survival distribution function was calculated by Kaplan-Meier equation (Kaplan and Meier 1958).
Results and discussion: The results of the study showed that reproductive disorders were the most common reason of culling in Holstein dairy cows (23.61%). Reproductive disorders like dystocia, retained placenta and problems related to calving, infertility, repeated abortion and other reproductive disorders are the most typical reason of culling (Ansari-Lari et al. 2012; Aziz Zadeh 2011; Heravi Moussavi et al. 2007). In this study, the second reason of culling were mastitis and problems related to udder (18.18%). When milk production increases, problems related to mastitis, reproductive disorders and health of dairy cow will increase (Abe et al. 2009). The third factor affecting culling was non-economical cow (12.48%).
The results showed that considered factors (season, age at first calving, parity, lactation stage and milk yield) had significant effect on risk of culling in Holstein cows (P<0.01). According to this result, cows with calving in warm seasons (spring and summer) in comparison to cows with calving could seasons (fall and winter) significantly had a high risk of culling (P<0.01). In consistent to Dechow and Goodling (2008), Pinedo and de Vries (2010) and Alvasen et al (2012) when cows calved in warm weather, they would have low survive in the herd. In this study, enhancing of the age at first calving leaded-in to increasing risk of culling and decreasing economical lifetime of Holstein dairy cows. The reasons of postpone of first calving usually were reproductive problems and low fertility that if it continues, the culling rate will increase for next period.
The risk of culling with ascending of parity significantly increased (P<0.01). Cows with 6th parity and higher had experienced high risk of culling than younger cows. Shahid et al (2015) in their study showed that increasing of Culling in old cow might be because of diseases related to high age.
The effect of lactation stage on risk of culling was significance (P<0.01). The risk of culling in mid lactation was lower than the early or late of lactation. Culling in the first stage of lactation is probably because of high stress in this stage when dairy cows touch high production, low feed intake and negative energy balance. This status lead to metabolic disorders like ketosis, displacement abomasum, acidosis, mastitis and the other diseases that can influence cow culling strongly. Reducing of culling risk was appeared with increasing of milk production (P<0.01). In High producing dairy cows, milk production is not determining factor for optional culling of cows. Pinedo et al (2010) and Shahid et al (2015) showed that the culling risk of cows declines with increasing of milk production.
According to Kaplan-Meier survival function, up to 1305 days from lifetime of cows, approximately 25% of Iranian Holstein dairy cows have been left the herd. Medium survival function, the time that 50% of cows have been culled, was 2068 days. Also, 75% of Iranian Holstein dairy cows, their length productive life were 2942 days.
Conclusion: According to the high culling rate in herds, in order to increasing lifespan and longevity of Holstein cows it is necessary to improve environmental conditions and management practices and, to control and manage factors affecting culling, to prevent and treat the diseases. Also, planning of selection programs in dairy cows based on health, fertility and mastitis traits is recommendable.
