EFFECT OF SUBCLINICAL KETOSIS ON DAILY MILK YIELD AND MILK COMPONENTS OF SLOVENIAN HOLSTEIN CATTLE

Cilj je ovog istraživanja bio utvrditi utjecaj supkliničke ketoze na dnevnu količinu i sastav mlijeka slovenskih holstein krava upotrebom podataka iz kontrole mliječnosti. Baza podataka osigurana od Kmetijskog inštituta Slovenije sastojala se od 1,299.630 test-day mjerenja količine mlijeka i sadržaja mliječne masti i bjelančevina 73,255 grla slovenskog holsteina prikupljenih od siječnja 2000. do prosinca 2005. godine. Krave su uzgajane na ukupno 5,333 gospodarstva u Sloveniji. Supklinička je ketoza indicirana omjerom između mliječne masti i bjelančevina višim od 1,5 u krava koje su imale dnevnu proizvodnju od 33 do 50 kg (Eicher, 2004). Ketoza indeks definiran je u odnosu na vrijeme proteklo od detekcije supkliničke ketoze do narednog kontrolnog dana. Utjecaj supkliničke ketoze na dnevnu količinu i sastav mlijeka analiziran je upotrebom miješanog statističkog modela zasebno za svaku laktaciju. Statistički je model uključivao fiksne utjecaje ketoza indeksa, godina-mjesec telenja, stadija laktacije te slučajni utjecaj životinje. Utvrđen je negativni utjecaj supkliničke ketoze na dnevnu količinu mlijeka, dnevni sadržaj mliječne masti, te na dnevnu količinu mliječne masti i bjelančevina u svim laktacijama. Pad proizvodnje utvrđen je unutar 35 dana po detekciji supkliničke ketoze te se nastavio pri sljedećim kontrolama. Pri analizi dnevnog sadržaja bjelančevina utvrđeno je povećanje pri kontrolama koje su uslijedile po detekciji. Rezultati provedenog istraživanja pokazuju da se podaci dobiveni kontrolom mliječnosti (test-day mjerenja) mogu upotrijebiti za ranu detekciju supkliničke ketoze.The objective of this study was to determine the effect of subclinical ketosis on daily milk yield and milk components in Slovenian Holstein cows using monthly test day records. Data provided by the Agricultural Institute of Slovenia consisted of 1,299,630 test-day records of milk, fat, and protein from 73,255 Slovenian Holstein cows collected from January 2000 to December 2005. Cows were reared on 5,333 farms in Slovenia. The subclinical ketosis was indicated by the fat to protein ratio higher than 1.5 in cows that yielded between 33 to 50 kg per day (Eicher, 2004). Only the first occurrence of upper defined criteria was considered in this study. The ketosis index was defined in relation to the timing of subclinical ketosis detection to the subsequent measures of test-day milk yields. The effects of subclinical ketosis on test day milk yield and milk components were studied separately for each parity using mixed model analysis. Statistical model included fixed effect of ketosis index, calving year-month, lactation stage and random effect of animal. Negative effect of subclinical ketosis on daily milk yield, daily fat content as well as on daily fat and protein yields was determined in each parity. Decrease was determined within 35 days after the detection of subclinical ketosis and continued in subsequent milk controls. When daily protein content was analysed, increase was determined in subsequent milk controls after detection. The research results show that test-day records could be used as a tool for early detection of subclinical ketosis