The Research Column

An 8 × 8 incomplete Latin square design was conducted with 48 lactating Danish Holstein cows over 6 periods of 21 days each. Eight diets were 2 × 2 × 2 factorially arranged: FAT (30 or 63 g crude fat/kg DM), NITRATE (0 or 10 g nitrate/kg DM), and 3-NOP (0 or 80 mg 3-NOP/kg DM), and cows were fed ad libitum. Milk samples were analyzed for general composition, fatty acids (FA) and thermal properties of milk fat.

Milk production data of 23 908 first lactation and multi lactation cows from 87 herds were used. Persistency was measured by a lactation curve characteristic decay, representing the time taken to halve milk production after peak yield. Decay was calculated for eight DPC (0, 30, 60, 90, 120, 150, 180, and 210 days after DIMc), which served as the dependent variable. Independent variables included DPC, DIMc (≤60, 61–90, 91–120, 121–150, 151–180, 181–210, >210 days), parity group, DPC × parity group, DPC × DIMc, and variables from 30 days before DIMc as covariates. 

Butters were produced using milks collected from three feeding systems: outdoor pasture grazing (high pasture allowance); indoor TMR (no pasture allowance); and a partial mixed ration (medium pasture allowance) system, which involved outdoor pasture grazing during the day and indoor TMR feeding at night. Butters were manufactured during early, mid, and late lactation.

A total of 42 Holstein heifer calves on a commercial dairy farm were enrolled in groups of three to different housing treatments; IH (n = 21) or GH (n = 21). Each treatment was composed of seven groups of three calves each. Calves in the GH treatment were housed in groups of three from six to ten days until 70 days of age. Individual pens consisted of one polyethylene hutch with a 1.5 m × 1.2 m outside exercise area. Group pens were constructed by assembling three polyethylene hutches with a 1.5 m × 3.6 m outside exercise area of wire panel fencing.

The authors measured AGEPprog, height, length, and BW in approximately 5 000 Holstein-Friesian or Holstein-Friesian × Jersey crossbred yearling heifers across 54 pasture-based herds managed in seasonal calving production systems.

Several other factors beyond temperature also affect heat exchange, including thermal radiation, air flow, and air moisture content. Although temperature is the primary driving force of heat exchange, it is generally agreed that temperature alone is not an adequate indicator of the environmental impact, because other factors can influence the perception of heat.

In recent years, the Montbéliarde (MO), Viking Red (VR), and Holstein (HO) breeds have been marketed for three-breed rotational crossbreeding. The MO and VR breeds have placed more selection emphasis on fertility, health, and longevity for decades than has the HO breed, while maintaining substantial selection emphasis on increased milk solids. Research on lactation-curve characteristics of crossbred dairy cows is however limited. Also, the persistency of production for MO-sired and VR-sired crossbred cows compared with their HO herdmates has not been studied.

The importance of obtaining greenhouse gas (GHG) and corresponding resource use data on dairy farms cannot be emphasised enough, as baseline data is required to evaluate where to put emphasis in mitigation or change. The publication from South-Western Sweden cited provides such an opportunity. The authors collected data and use Life Cycle Assessment (LCA) methodology in analysis. The purpose of the study was to gain knowledge of the environmental impact of contemporary milk production and how farms differ in resource use and emissions.

Of the newer developments are the availability of high-dimensional omics, such as the metagenome, metabolome and transcriptome, which provide the opportunity to incorporate such data, in addition to genomic data, to improve the prediction of feed efficiency. The inclusion of microbial data in genomic models enables unravelling the contribution of a particular host genome and its microbiome to the phenotype of interest.

For a food to be considered a good source of calcium (Ca), it must have a high Ca concentration and the Ca must be highly bioavailable. Dairy products have traditionally been considered excellent sources of Ca due to both a high Ca density and bioavailability. For example, a glass of 240 mL milk is estimated to contain 300 mg Ca, providing about 96 mg absorbable Ca and a bioavailability of 30 %, which is considered to be high.