SUMMARYOverfeeding minerals to dairy herds will raise diet cost, increase their excretion into the environment and for minerals such as copper (Cu) can lead to poisoning and cow death. In contrast, underfeeding may compromise cow performance, health and fertility. Despite this, the level of mineral intake on commercial dairy units is poorly documented. To determine the mineral intake on commercial dairy herds in central and northern England over the winter of 2011/12 and compare these to recommended levels, samples of compound feed, forage mix, supplementary sources (including lick blocks, rumen boluses, free access minerals and drenches) and drinking water were collected from 50 herds over the winter feeding period and analysed for 10 macro and trace minerals. For cows in early lactation the mean dietary concentration of phosphorus (P) was 4·5 g/kg dry matter (DM) (s.d. 0·70), 0·1 g/kg DM below UK requirements, and for calcium (Ca) was 10·2 g/kg DM (s.d. 2·94), 5·9 g/kg DM above requirements. Trace mineral concentrations were also in excess of requirements in early lactation, with a mean dietary Cu concentration of 28 mg/kg DM (s.d. 9·85), approximately 18 mg/kg DM above UK requirements, with 32 of the 50 herds feeding above the UK industry recommended maximum of 20 mg/kg DM and 6 above the EU limit of 40 mg/kg DM. Dietary mineral concentrations were generally lower in late lactation but still higher than requirements. The forage mix (including supplementary feeds and minerals) contributed the greatest amount of minerals, with percentile ranges (10th–90th) of 2·1–4·4 g/kg diet DM for P, 1·4–3·2 g/kg diet DM for magnesium (Mg) and 5·3–25·0 mg/kg diet DM for Cu. Compounds fed in the milking parlour supplied (10th–90th percentile) 0·0–1·4 g P g/kg diet DM, 0·0–1·2 g Mg/kg diet DM and 0·0–11·6 mg Cu/kg diet DM. For the upper 90th percentile of dairy herds, water supplied proportionally 0·08 of Ca requirements recommended in early lactation in the UK, whilst supplementary mineral sources supplied up to 0·64 of Cu and 0·43 of zinc (Zn) requirements. High dietary concentrations of Cu were not justified by the presence of the dietary antagonist molybdenum (Mo), with no relationship between the two minerals in early or late lactation diets. In conclusion, most dairy herds were feeding excess amounts of minerals over the winter feeding period when compared to UK or other national recommended guidelines, with the implications of a higher diet cost and negative impact on the environment and animal health.

The effect of winter feeding system on the periparturient performance and early milk production and metabolism of pregnant Holstein‐Friesian dairy heifers destined for a high‐output, total mixed ration (TMR)‐based system was examined. Forty‐eight, 23 ± 0.4‐month‐old, in‐calf Holstein‐Friesian heifers were assigned to one of three treatments: out‐wintered on perennial ryegrass and grass silage (G), out‐wintered on fodder beet and grass silage (F) or housed and fed grass silage and concentrate (H). The study commenced in November 2013, with heifers on treatment for 91 days, housed from 6 weeks prior to parturition and fed a dry cow TMR. Postpartum performance and metabolism were monitored for 12 weeks. Prepartum, average daily gain was lower in heifers receiving G at 0.95 kg d−1 cow−1 than F or H (1.24 and 1.11 kg d−1 cow−1 respectively). Body condition score of heifers that received G was also lower compared with treatments F or H both pre‐ and postpartum. Prepartum, plasma β‐hydroxybutyrate concentrations were lowest in animals receiving treatment H, highest in F and intermediate in G, but did not differ between treatment postpartum. Milk yield averaged 30.7 kg d−1 cow−1 and was not affected by treatment, but milk fat content was lowest in animals that received F (35.4, 37.1 and 37.9 g/kg for F, G and H respectively). The results indicate that out‐wintering in‐calf dairy heifers on fodder beet or perennial ryegrass is a viable alternative to winter housing in high‐output TMR‐based milk production systems in a temperate region.

The effects of a cobalt (Co), copper (Cu), selenium (Se), and iodine (I) tracemineral ruminal bolus on the mineral status and performance of out-wintered, pregnant dairy heifers was investigated. Nine commercial farms grazing pasture (G), kale (K), or fodder beet (F) were used (n=3 per forage), with forty heifers on each farm randomly allocated to not receive (B-) or receive (B+) two combined mineral boluses. Mean plasma Co concentrations were 0.021 and 0.041 µmol/L in Band B+ respectively (p < 0.001), with serum vitamin B12 also higher in heifers receiving B+ than B-(p < 0.001). Mean plasma Se concentration was 0.50 and 0.82 µmol/L in Band B+ respectively, with heifers that received B+ also having a higher (p < 0.05) mean blood GSH-Px concentration (30 and 76 U/mL haematocrit in Band B+ respectively). Providing a mineral bolus did not affect plasma Cu concentration in heifers receiving G or F (p < 0.05), but was higher in KB+ compared to KB-(p < 0.05) at the middle and end of the out-wintering period. Heifers receiving KB-also had a lower haemoglobin and red blood cell count, but a higher mean corpuscular volume than KB+ at the end of the out-wintering period. Animals receiving B-had a higher plasma thyroxine concentration (p < 0.05). Neither the bolus nor forage type affected body weight (p > 0.05), however condition score was higher (p < 0.05) in B+ at the end of the study. It is concluded that the provision of a trace mineral bolus increased plasma concentrations of the minerals supplied, with the greatest benefits in animals grazing kale, but these increases were not translated into improved performance.

The effects of a limited grazing period on the performance, behaviour and milk composition of high‐yielding dairy cows were examined. A total of 56 Holstein cows yielding 44.7 ± 0.42 kg/day were allocated to one of four treatments in one of two, 4‐week periods. Treatments were as follows: control (C)—cows housed and offered TMR ad libitum; early grazing (EG)—cows grazed for 6 hr after morning milking then housed; delayed grazing (DG)—cows returned to housing for 1 hr after morning milking followed by grazing for 6 hr, then housed; restricted TMR (RT)—cows grazed for 6 hr after morning milking, then housed and fed TMR at 75% of ad libitum. Intake of TMR was highest in cows receiving C, intermediate in EG and DG, and lowest in RT at 26.9, 23.6, 24.7 and 20.3 kg DM/day respectively. Pasture intake was similar in cows receiving EG or DG, but was higher in RT at 2.4, 2.0 and 3.5 kg DM/day respectively. Milk yield was similar between cows receiving C, EG or DG, but lowest in RT at 45.7, 44.2, 44.9 and 41.7 kg/cow, respectively, while milk fat content of C18:3 n‐3 was increased by grazing. Cows in C spent more than 55 min/day longer lying and had three additional lying bouts/day, while lying bouts were shorter than for cows receiving EG, RT or DG. It is concluded that high‐yielding cows can be grazed for 6 hr/day with little impact on performance, provided TMR is available ad libitum when housed.

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