Differences In Fat Yields Research Articles

Milking-to-Milking Variability for Milk Yield, Fat and Protein Percentage, and Somatic Cell Count

The main objectives were to analyze milking-to-milking variability in milk yield, fat and protein percentages, and somatic cell count (SCC). Additional objectives were to investigate the factors that affect variation in milk fat percentage and to study the seasonal variations in milk, fat, and protein yields and SCC. A total of 16 farms (14 milked 2× and 2 milked 3×) across Canada participated in a 5-d milk-sampling study, with 27,328 milk samples collected and analyzed for fat and protein yields and SCC. Descriptive statistics for both 2× and 3× herds for milk yield and fat and protein percentages followed a typical pattern throughout lactation, and the somatic cell linear scores were higher in early lactation for first-lactation cows (4.7 vs. 3.8) but were higher at the end of lactation for cows in second lactation or greater (5.1 vs. 4.9). The 2× herds had higher milk yields in the morning (∼17 vs. ∼14kg), whereas the 3× herds had the lowest milk yields in the morning, and yields peaked at the evening milking (∼9 vs. ∼11.2kg). A herd management questionnaire was distributed to participating producers to investigate the relationship between management variables and variations in milk fat percentage over the 5-d sampling period. Data from the questionnaire determined that milking period had a significant effect on milk fat in 2× herds, with fat percentage 1.11% lower in the morning compared with the evening milking period. Seasonal differences in milk, fat, and protein yields were investigated in 910 cows on 3 farms, with 5,517 fat and 5,534 protein samples. The seasonal differences in fat yield [summer = 1.02±1.05kg/d (SEM); winter = 1.19±1.05kg/d] and protein yield (summer = 0.85±1.05kg/d; winter = 0.96±1.05kg/d) were significant only for first lactation. Understanding the variability in milk yield, fat and protein percentages, and SCC is important when making management decisions and in milk-recording programs.

A Genome Scan To Identify Quantitative Trait Loci Affecting Economically Important Traits in a US Holstein Population

Quantitative trait loci affecting economically important traits were studied for eight large US Holstein grandsire families by using the granddaughter design. A total of 155 microsatellite markers located throughout the bovine genome were selected for the scan. The data analyzed include genotypes for 50 markers not previously reported. Results analyses of 105 marker genotypes reported previously were updated. Effects of marker alleles were analyzed for 38 traits including traits for milk production, somatic cell score, productive life, conformation, calving ease, and 16 canonical traits derived from conformation and production traits. Permutation tests were used to calculate empirical traitwise error rates. A traitwise critical value of P = 0.1 was used to determine significance. Ten putative quantitative trait loci associated with seven of the new markers were identified within specific families. One marker on chromosome 14 was associated with differences in fat yield, fat percentage, and a canonical production trait in two families. Markers on chromosomes 18 and 22 were associated with differences in rump angle in the same family. Markers were associated with differences in udder depth and fore udder attachment on chromosomes 16 and 20, respectively. One marker on chromosome 27 was associated with a difference in the dairy capacity composite index, and another marker on chromosome 13 was associated with a difference in a canonical conformation trait. These additional markers complete our genome scan to identify quantitative trait loci affecting economically important traits in a selected commercial Holstein population. The quantitative trait loci identified in this genome scan may be useful for marker-assisted selection to increase the rate of genetic improvement on traits such as disease resistance and conformation traits associated with fitness while accelerating genetic improvement for production.

Forage Growth and Performance of Grazing Dairy Cows Supplemented with Concentrate and Chopped or Long Hay

Holstein and Brown Swiss cows were in three groups of eight in a 3×3 Latin square design with 4-wk periods. Cows averaged 88 d in lactation at start of trial. All cows simultaneously grazed grass and clover pastures on a rotational basis. Supplement treatments were concentrate (A), concentrate with 10% added chopped hay (B), and concentrate plus 1kg long hay/cow daily (C). Concentrate was offered at 1 kg/3kg 4% fat-corrected milk to cows on A and C, and 1 kg/2.7kg to those on B. Forage growth, amounts available for grazing, and average dry matter intake were measured by clipping subsamples prior to and after each grazing and by use of cages placed in the field.Milk yields and milk fat percentages were 27.1, 3.34; 27.9, 3.32; and 28.3, 3.20 for treatments A, B, and C, respectively. Differences between A and C were significant. Milk fat percentage decreased moderately when cows first went to pasture.There were no treatment differences in fat yield, milk protein percentage, yield of fat-corrected milk, rumen fluid composition, or body weight gain.Available forage per cow exceeded 22kg dry matter/cow daily except during one 10-d period toward the end of the trial when it amounted to 16.6kg. Intake of dry matter from pasturage, measured by the sward cutting technique, averaged 14.5kg./cow daily over the 12 wk.

The significance of differences in levels of feeding, before and after calving, on milk yield under intensive grazing

The effects of varying the plane of nutrition immediately before and after calving on milk yield, milk composition, live-weight change, and feed intake were examined. In each of two years, individual members of 30 sets of identical twins were fed either to gain approximately 0.7 kg live weight daily, or to maintain live weight during the last 4 weeks of pregnancy. After calving, one half of the cows on each treatment was grazed at a medium (4.1 cows/ha) or a heavy (4.9 cows/ha) stocking rate. At the end of the first 8 weeks of lactation, butterfat yields were 21% and 15% higher in successive years for cows which gained weight than for those which merely maintained weight in the last month of pregnancy. Differences in fat yields associated with intensity of grazing after calving were significant in the second trial only. There were significant differences in milk composition associated with pre-calving feeding, but no significant interactions between pre- and post-calving treatments for milk yield or milk ...