Kortare sintid – hur påverkar det kons mjölkavkastning, metabolism, hälsa, hull och vikt?

Abstract: A shorter dry period length has in studies abroad showed some positive effects among high yielding dairy cows. Among other things it has been suggested that the periparturient metabolic stress becomes lower, that the fertility is improved and dry off becomes gentler for the udder, due to a lower milk yield. The milk yield is generally reduced during the first period after calving, especially among primiparous cows. The aim of this master thesis was to investigate how Swedish cows were affected by a shortened dry period, regarding milk yield, metabolism, health, body condition and body weight from two months before calving to some weeks after calving. Also plasma concentration of lactose during the period before calving was determined. Two breeds were included in the study, Swedish Red cows (SRB) and Swedish Holsteins (SH). This study was part of a larger research project which also covers additional aspects like fertility, feed intake and milk composition. The present literature review also includes these aspects. All cows at Lövsta Research Centre with expected calving date from 20 September 2012 to 28 February 2013 were included in the study, as long as the cows did not need dry period antibiotic treatment and had a milk yield that exceeded 15 kg/day 10 weeks before expected calving. The cows were divided into two groups, one with a dry period of eight weeks (n=15) and one with a dry period of four weeks (n=17). We tried to get the groups as similar as possible regarding breed and parity of the cows. Blood was collected 8, 4, 2, and 1 week prepartum and 1, 2, 3, 4, 6, 9 and 12 weeks postpartum. Body condition and weight were registered once a month, in other words 8 and 4 weeks prepartum, some days after parturition and 4, 8 and 12 weeks postpartum. The blood samples were analysed for glucose, non-esterified fatty acids, insulin, insulin growth factor 1 and lactose. The insulin sensitivity was thereafter determined based on the concentrations of glucose, insulin and non-esterified fatty acids. The small number of animals in this study limited the possibilities to draw conclusions from it. Preliminary results indicated that multiparous SRB cows were less adaptive towards a shorter dry period than multiparous SH cows, because their milk yield were lower in late lactation. An extra amount of milk was generated from the cows with shortened dry period in late lactation. On average 480 kg/cow was generated during the four weeks of extra milking. However the cows with shorter dry period had a lower milk yield in early lactation. The glucose concentration in plasma was higher and a tendency to lower concentrations of non-esterified fatty acids was seen among the cows with shortened dry period during the week after parturition. This may indicate an improved energy balance among cows with a shorter dry period in the early stage of lactation. No effects of dry period length on health were seen in the subset of animals included in the master thesis. Assuming that the lactose synthesis did not differ between the two treatment groups, the permeability of tight junctions was not affected by treatment. SRB cows with short dry period did not lose body condition and weight after parturition, while SH cows with shortened dry period and cows of both breeds with a dry period of eight weeks did. The larger research project about dry period length that includes more cows and more aspects of a shortened dry period will show if the tendencies that were seen here will last, and if a shorter dry period is positive for at least some of the Swedish cows.