Uticaj toplotnog stresa na hormonalni status krava u periodu laktacije

Abstract

Cilj ovog rada bijo je da se ispita uticaj toplotnog stresa na metabolički i endokrini status krava. Ogled je izveden na 20 krava Holštajn – frizijske rase od 18. do 45. dana laktacije tokom letnjeg perioda u trajanju od 37 dana. Tokom perioda izvođenja ogleda određivana je vrednost „satnih“ toplotnih indeksa (THI) a zatim izračunata vrednost prosečnih jutarnjih (od 22 h prethodnog do 9 h tekućeg dana), popodnevnih (od 10 h do 21 h tekućeg dana) i celodnevnih THI. Uzorkovanje krvi i određivanje trijasa izvršeno je 1., 2., 8., 11., 14., 18., 25., 29. i 37. dana ogleda, u jutarnjem i popodnevnom periodu. Na osnovu vrednosti satnih THI ceo ogledni period je podeljen na tri perioda: period A u kome su krave bile izložene izrazitom toplotnom stresu (THI ≥ 78) najmanje 7 sati u toku 24 sata (1., 8., 14., i 37. dan ogleda); period B u kome su krave bile izložene umerenom toplotnom stresu (72 ≥ THI ≤ 78) najmanje 7 sati u toku 24 sata (2., 18., i 29. dan ogleda); period C u kome krave nisu bile izložene toplotnom stresu (THI ≤ 72) u toku 24 sata (11. i 25. dana ogleda). Prosečni dnevni THI u periodu A (73,25 ± 0,89) je bio značajno veći (p<0,01, pojedinačno) u odnosu na period B (71,45 ± 0,96) i period C (65,41±2,09). THI u periodu B je bio značajno viši nego u periodu C (p<0,01). Dnevni unos hrane je bio manji kod krava tokom perioda izloženosti toplotnom stresu za 2,9 odnosno 1,74 kg SM obroka u odnosu na period kada su bile u optimalnim ambijentalnim uslovima držanja. U periodu optimalnih ambijentalnih uslova temperature prosečna dnevna mlečnost je bila značajno viša (43,08 ± 5,15 L), nego u uslovima umerenog (41,96 ± 5,51 L) odnosno izrazitog toplotnog stresa (39,47 ± 5,15 L) ali ovo smanjenje mlečnosti nije bilo u skladu sa količinom nepojedene hrane. Hipertermija (39,72 ± 0,47 °C) i tahipnoja (86,60±6,39 n/minut) kod krava su ustanovljene samo u popodnevnim časovima i mogu da posluže kao pouzdani klinički poklazatelj toplotnog stresa. Pokazatelji razvoja toplotnog stresa su i promene vrednosti elektrohemijske reakcije krvi (alkaloza). Koncentracija koritzola je bila povišena u uslovima umerenog (10,44±3,07 nmol/L) i izrazitog topolotnog stresa (8,74±2,49 nmol/L) u odnosu na period sa optimalnim ambijentalnim temperaturnim uslovima (6,41±2,11 nmol/L), pri čemu su razlike u koncentracijama ovog hormona bile značajne između svih ispitivanih perioda (p<0,01, pojedinačno)...

The aim of this study was to evaluate the effects of heat stress on the metabolic and endocrine status in cows. The experiment was performed on 20 Holstein Friesian cows from lactation day 18 to 45 during the summer period for a duration of 37 days. During the experiment the „hourly“ heat indices (THI) and thereon the values of the average morning (from 10PM the previous day to 9AM of the current day), afternoon (10AM to 9PM of the current day) and overall daily THI were determined. Blood sampling and trias readings were recorded on the 1st, 2nd, 8th, 11th, 14th, 18th, 25th, 29th and 37th day of the experiment, in the morning and afternoon periods. According to the values for hourly THI the entire experimental period was divided into three periods: period A in which the cows were exposed to a severe heat stress (THI ≥ 78) at least for 7 hours during a 24h period (1st, 8th, 14th and 37th day of the experiment); period B during which the cows were exposed to moderate heat stress (72 ≥ THI ≤ 78) at least for 7 hours during a 24h period (2nd, 18th, and 29th day of the experiment), period C during which the cows were exposed to heat stress (THI ≤ 72) during 24h (11th and 25th experimental day).The average daily THI for period A (73,25 ± 0,89) was significantly higher (p<0.01, individually) compared with period B (71.45 ± 0.96) and period C (65.41±2.09), during period B THI was significantly higher compared with period C (p<0.01). The daily feed intake was by 2.9 and 1.74 kg DM feed less in cows exposed to heat stress compared with the period in which the cows were kept under optimal ambient conditions. In the period with optimal environmental temperature conditions the average milk yield was significantly higher (43.08 ± 5.15 l), than in conditions of moderate (41.96 ± 5.51) and severe heat stress (39.47 ± 5.15). However, this decrease was not in unison with the quantity of not eaten feed. Hyperthermia (39.72 ± 0.47 °C) and tahipnoa (86.60±6.39 n/min) were recorded only during the afternoon hours in the cows exposed to severe heat stress and can be used as reliable clinical indicators of heat stress. Indicators of arising heat stress are the changes in blood electrochemical reaction (alkalosis), also...