Effect of dry period length on plasma minerals and oxidative stress around parturition and milk yield in high-producing Holstein dairy cows.

The aim of present study was to evaluate the effect of dry period length (56 vs. 28 days) on plasma minerals, albumin, total protein and globulin, oxidative status, and milk production in high-producing dairy cows (13,500 ± 1800 kg milk in previous 305-day lactation). A total of 120 multiparous Holstein cows were used in a repeated measurement mixed model (animal was considered random effect) with two experimental groups and 60 replicates each: 1-long dry period (LDP, 56-day dry period) and 2-short dry period (SDP, 28-day dry period). While LDP cows received two different rations in far-off and close-up periods (DCAD = 189 and - 130 Meq/Kg, respectively), the SDP cows received only the close-up ration (- 130 Meq/Kg) without passing the far-off stage. Blood samples for minerals, oxidative stress, and metabolites (albumin, total protein) were collected on calving day, 24 and 48 h after parturition. Milk samples of all cows in each group were collected monthly (four months from parturition to 120 DIM) and analyzed for milk fat, protein, and somatic cell count (SCC). Results showed that SDP had no effect on plasma calcium (Ca), ionized calcium (iCa), magnesium (Mg), and phosphorus (iP). Total antioxidant capacity (TAC) in the SDP cows was higher (P < 0.05) than the LDP cows. The treatment had no significant effect on plasma concentration of total protein, albumin, globulin, and superoxide dismutase (SOD) activity. A positive significant (P < 0.05) correlation was observed between plasma Mg and TAC in SDP group. Short dry period reduced (P < 0.05) milk production (48.39 vs. 51.95 kg/day; about 7%) during the first 120 days in milk. However, SDP cows had higher (P < 0.05) milk protein content compared to LDP group. The log-transformed of somatic cell count (LnSCC) was not affected by the treatment. It was concluded that a short dry period (28 days) had no negative effect on plasma Ca, iCa, Mg, and iP and even could improve TAC in high-producing Holstein cows.

Rates of inbreeding and genetic diversity in Iranian Holstein cattle.

The accumulation of inbreeding and the loss of genetic diversity is a potential problem in Holstein dairy cattle. The goal of this study was to estimate inbreeding levels and other measures of genetic diversity, using pedigree information from Iranian Holstein cattle. Edited pedigree included 1,048,572 animals. The average number of discrete generation equivalents and pedigree completeness index reached 13.4 and 90%, respectively. The rate of inbreeding was 0.3% per year. Effective number of founders, founder genomes, non-founders and ancestors of animals born between 2003 and 2011 were 503, 15.6, 16.1 and 25.7, respectively. It was proven that the unequal founder contributions as well as bottlenecks and genetic drift were important reasons for the loss of genetic diversity in the population. The top 10 ancestors with the highest marginal genetic contributions to animals born between 2003 and 2011 and with the highest contributions to inbreeding were 48.20% and 63.94%, respectively. Analyses revealed that the most important cause of genetic diversity loss was genetic drift accumulated over non-founder generations, which occurred due to small effective population size. Therefore, it seems that managing selection and mating decisions are controlling future co-ancestry and inbreeding, which would lead to better handling of the effective population size.