Özge AKKUŞ, VOLKAN SEVİNÇ, Çiğdem TAKMA, Öznur İŞÇİ GÜNERİ

Estimation of Parametric Single Index Ordered Logit Model on Milk Yields

This article aims to determine some important factors affecting the milk yield of Holstein Friesian cows and introduce the use of single index ordered logit model in milk yield studies. Considering the three-level ordered structure of the dependent variable of milk yield, a single index ordered logit model is applied to the data set. The data set used in this study is consisted of the 305-day milk records of the Holstein Friesian cows that calved between 2001-2011 years. 14487 records, obtained from 1840 herds belonging to the members of Cattle Breeders Association in Isparta province, Turkey, are analyzed. The direct effects of the variables: parity, lactation length, first year of calving and calving season on milk yield are investigated and comprehensive interpretations are presented. Results show that the cows having longer lactation lengths produce more milk than the cows having middle lactation lengths. The highest amount of milk yield is produced by the cows calving for the first time in their middle ages and in autumn season. The amount of milk obtained after a birth occurring in spring season is higher than the one reached after a birth in summer. Cow being on its 1st parity decreases the milk yield compared to the 6th parity. This result is consistent with the finding in literature in that cows reach their highest amount of milk on their 4th parities.

Süt Veriminde Parametrik Tek İndeks Sıralı Lojit Model Tahmini

Bu makale, Holstein Friesian ineklerinin süt verimini etkileyen bazı önemli faktörleri belirlemek ve süt verimi çalışmalarında tek indeks sıralı lojit modelin kullanımını tanıtmayı amaçlamaktadır. Süt verimi bağımlı değişkeninin üç düzeyli sıralı yapısını göz önünde bulundurarak, veri setine tek indeks sıralı lojit model uygulanmıştır. Bu çalışmada kullanılan veriler 2001-2011 yılları arasında buzağılayan Holstein Friesian ineklerinin 305 günlük süt kayıtlarından oluşmaktadır. Isparta ilinde bulunan Sığır Yetiştiricileri Birliği üyelerine ait 1840 sürüden elde edilen 14487 kayıt analiz edilmiştir. Parite, laktasyon süresi, ilk buzağılama yılı ve buzağılama mevsimi değişkenlerinin süt verimi üzerindeki doğrudan etkileri araştırılmış ve sonuçların ayrıntılı yorumlarına yer verilmiştir. Sonuçlar daha uzun laktasyon süresine sahip olan ineklerin, orta laktasyon süresine sahip olan ineklerden daha fazla süt ürettiğini göstermektedir. Orta yaşlarında ve sonbahar mevsiminde ilk kez buzağılayan inekler en yüksek düzeyde süt üretmektedir. İlkbahar mevsiminde meydana gelen bir doğumdan sonra elde edilen süt miktarı, yazın doğumdan sonra ulaşılan miktardan daha yüksektir. Birinci paritesindeki ineklerin süt verimi 6. pariteye göre azalır. Bu sonuç, ineklerdeki en yüksek süt miktarının 4. paritede elde edildiği yönündeki literatürde yer alan bulguyla tutarlıdır..

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