title: Extending lactation in pasture-based dairy cows: I. Genotype and diet effect on milk and reproduction.
abstract: The aim of this study was to test the feasibility of extended lactations in pastoral systems by using divergent dairy cow genotypes [New Zealand (NZ) or North American (NA) Holstein-Friesian (HF)] and levels of nutrition (0, 3, or 6 kg/d of concentrate dry matter). Mean calving date was July 28, 2003, and all cows were dried off by May 6, 2005. Of the 56 cows studied, 52 (93%) were milking at 500 d in milk (DIM) and 10 (18%) were milking at 650 DIM. Dietary treatments did not affect DIM (605 +/- 8.3; mean +/- SEM). Genotype by diet interactions were found for total yield of milk, protein, and milk solids (fat + protein), expressed per cow and as a percentage of body weight. Differences between genotypes were greatest at the highest level of supplementation. Compared with NZ HF, NA HF produced 35% more milk, 24% more milk fat, 25% more milk protein, and at drying off had 1.9 units less body condition score (1 to 10 scale). Annualized milk solids production, defined as production achieved during the 24-mo calving interval divided by 2 yr, was 79% of that produced in a normal 12-mo calving interval by NZ HF, compared with 94% for NA HF. Compared with NZ HF, NA HF had a similar 21-d submission rate (85%) to artificial insemination, a lower 42-d pregnancy rate (56 vs. 79%), and a higher final nonpregnancy rate (30 vs. 3%) when mated at 451 d after calving. These results show that productive lactations of up to 650 d are possible on a range of pasture-based diets, with the highest milk yields produced by NA HF supplemented with concentrates. Based on the genetics represented, milking cows for 2 yr consecutively, with calving and mating occurring every second year, may exploit the superior lactation persistency of high-yielding cows while improving reproductive performance.
authors.affiliation: Dexcel, Private Bag 3221, Hamilton, New Zealand. eric.kolver@synlait.co.nz
authors.forename: E S
authors.initials: ES
authors.lastname: Kolver
authors.forename: J R
authors.initials: JR
authors.lastname: Roche
authors.forename: C R
authors.initials: CR
authors.lastname: Burke
authors.forename: J K
authors.initials: JK
authors.lastname: Kay
authors.forename: P W
authors.initials: PW
authors.lastname: Aspin
mesh_terms: D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena / Q000235:genetics / Q000502:physiology*; D000818:Animals; D001835:Body Weight / Q000502:physiology; D002417:Cattle / Q000235:genetics* / Q000502:physiology*; D005260:Female; D005838:Genotype; D006304:Health Status; D007774:Lactation / Q000235:genetics / Q000502:physiology*; D008055:Lipids / Q000032:analysis; D008892:Milk / Q000737:chemistry / Q000378:metabolism; D008894:Milk Proteins / Q000032:analysis; D006109:Poaceae; D011247:Pregnancy; D018873:Pregnancy Rate; D012098:Reproduction / Q000235:genetics / Q000502:physiology*; D013997:Time Factors
chemical_list: D008055:Lipids; D008894:Milk Proteins