D.E. Beever

Nitrogen pollution by dairy cows and its mitigation by dietary manipulation

One of the major contributions to atmospheric pollution comes from nitrogen (N) derived from cattle and especially dairy cows. Although most estimates of ammonia volitilization are based on total N excretion, it has been repeatedly shown that urinary N is a much more important source of pollution than faecal N, specially under grazing conditions. A model was developed to predict the amount and form of N excreted under different production systems. Analysis of N pollution was based on data collected from Holstein/Friesian cows fed 30 different diet types consisting of 10 grass silages and 6 concentrates. While there was a strong correlation between N intake and N output in general, urinary N was exponentially correlated with N intake and the model predicted about 80% loss of N in urine for levels of N consumption above 500 g N/d. On the other hand, outputs of faecal and milk N increased by less than 20% per unit increase in N intake. Model predictions also agreed well with published data and provided reasonable estimates of the form in which N was excreted. Concentrate composition with respect to energy type and its degradation and protein degradability and silage type had significant effects on the amount and form of N excreted. It is concluded that N pollution may be ameliorated by using grass grown with moderate fertiliser application, and maize-based energy supplements, formulated to provide low degradable protein and with N intakes of less than 400 g/d for average yielding cows.

Effect of forage type and proportion of concentrate in the diet on milk fatty acid composition in cows given sunflower oil and fish oil

Based on the potential benefits of cis-9, trans- 11 conjugated linoleic acid (CLA) for human health there is a need to develop effective strategies for enhancing milk fat CLA concentrations. In this experiment, the effect of forage type and level of concentrate in the diet on milk fatty acid composition was examined in cows given a mixture of fish oil and sunflower oil. Four late lactation Holstein-British Friesian cows were used in a 4 x 4 Latin-square experiment with a 2 x 2 factorial arrangement of treatments and 21-day experimental periods. Treatments consisted of grass (G) or maize (M) silage supplemented with low (L) or high (H) levels of concentrates (65: 35 and 35: 65; forage: concentrate ratio, on a dry matter (DM) basis, respectively) offered as a total mixed ration at a restricted level of intake (20 kg DM per day). Lipid supplements (30 g/kg DM) containing fish oil and sunflower oil (2: 3 w/w) were offered during the last 14 days of each experimental period. Treatments had no effect on total DM intake, milk yield, milk constituent output or milk fat content, but milk protein concentrations were lower (P = C20 (n-3) polyunsaturated fatty acids (PUFA) and lower (P = C20 (n-3) PUFA content, but reduced (P 0.05) on total milk conjugated linoleic acid (CLA) (2.7 and 2.8 g/100 g fatty acids, for M and G, respectively) or cis-9, trans-11 CLA content (2.2 and 2.4 g/100 g fatty acids). Feeding high concentrate diets tended (P<0.10) to decrease total CLA (3.3 and 2.2 g/100 g fatty acids, for L and H, respectively) and cis-9, trans-11 CLA (2.9 and 1/7 g/100 g fatty acids) concentrations and increase milk trans-9, cis-11 CLA and trans-10, cis-12 CLA content. In conclusion, the basal diet is an important determinant of milk fatty acid composition when a supplement of fish oil and sunflower oil is given.

The effect of crop maturity on the nutritional value of maize silage for lactating dairy cows 3. Food intake and milk production.

Fifty-five multiparous Holstein-Friesian cows were used in a 20-week continuous design study to determine the effect of maize silage maturity on food intake and milk production. Forage maize ( cv. Hudson) was harvested and ensiled at target dry matter (DM) contents of 230 (T23), 280 (T28), 330 (T33) and 380 (T38) g per kg fresh weight (FW). The mean values for volatile-corrected DM (VCDM), starch, neutral-detergent fibre (NDF), crude protein and predicted metabolizable energy (ME) content of the four maize silages were 226, 290, 302 and 390 g/kg FW, 114, 274, 309 and 354 g/kg VCDM, 574, 447, 431 and 448 g/kg VCDM, 96, 80, 74 and 75 g/kg VCDM and 10·3, 11·5, 11·6 and 11·2 MJ/kg DM, respectively. Grass silage containing 296 g VCDM per kg FW was produced from the primary growth of a perennial ryegrass sward. At week 3 of lactation cows were allocated to one of five forage treatments offered ad libitum. The forage treatments were either grass silage alone (TGS) or a 3 : 1 DM ratio of maize and grass silage designated as T23, T28, T33 and T38. All cows also received 8·7 kg DM per day of a dairy concentrate. Forage VCDM intake for TGS was lower ( P P P P P P P P P > 0·05) milk protein content, protein yield was higher ( P

Diet Digestibility, Rate of Passage, and Eating and Rumination Behavior of Jersey and Holstein Cows

Diet digestibility and rate of passage, eating and rumination behavior, dry matter intake (DMI), and lactation performance were compared in 6 Jersey and 6 Holstein multiparous cows. Cows were fed gestation diets according to body weight (BW) beginning 7 wk before expected calving and ad libitum amounts of a lactation diet postpartum. Diet digestibility and rate of passage were measured in 5-d periods at wk 5 prepartum and wk 6 and 14 of lactation. Eating and ruminating behavior was measured over 5-d periods at wk 5 and 2 prepartum and wk 2, 6, 10, and 14 of lactation. Milk yield and DMI were higher in Holsteins, but milk energy output per kilogram of metabolic BW (BW(0.75)) and intake capacity (DMI/kg of BW) did not differ between breeds. Holsteins spent longer ruminating per day compared with Jerseys, but daily eating time did not differ between breeds. Jerseys spent more time eating and ruminating per unit of ingested feed. The duration and number of meals consumed did not differ between breeds, but the meals consumed by Jerseys were distributed more evenly throughout each 24-h period, providing a more regular supply of feed to the rumen. Feed passed through the digestive tract more quickly in Jerseys compared with Holsteins, suggesting particle breakdown and rumen outflow were faster in Jerseys, but this may also reflect the relative size of their digestive tract. Neutral detergent fiber digestibility was greater in Jerseys, despite the shorter rumen retention time, but digestibility of dry matter, organic matter, starch, and N did not differ between breeds. Utilization of digested N for tissue retention was higher at wk 5 prepartum and lower at wk 14 of lactation in Jerseys. In contrast to numerous published studies, intake capacity of Jerseys was not higher than that of Holsteins, but in the present study, cows were selected on the basis of equal expected milk energy yield per kilogram of metabolic BW. Digestibility of neutral detergent fiber and rate of digesta passage were higher in Jerseys, probably as a consequence of increased mastication per unit of feed consumed in Jerseys and their smaller size.

Detection of transgenic DNA in milk from cows receiving herbicide tolerant (CP4EPSPS) soyabean meal

Abstract Ten Holstein/Friesian cows with an average liveweight of 630 kg and producing 25.3 kg milk/day received a total mixed ration (TMR) in which the forage component formed 55% of total DM and contained non-genetically modified (GM) grass and maize silage in a 1:3 DM ratio. In study weeks 1–3 the TMR DM also contained non-GM supplements of 18.5% cracked wheat and 26.1% rapeseed meal. In weeks 4–12 soyabean meal, genetically modified (CP4EPSPS) to be herbicide tolerant, replaced rapeseed meal at 26.1% of the total diet in weeks 4–5 and 13.9% of the total diet in weeks 6–12. Weekly milk samples were taken from all cows. Samples were spiked with DNA extracted from the soyabean meal to establish the limit of detection (LOD) of transgenic DNA using a polymerase chain reaction (PCR) analyses designed to detect transgenic DNA fragments smaller than 200 bp. Subsequent PCR analyses carried out in duplicate on TMR and milk samples collected at weeks 3, 4 and 12 of the study used three DNA primer sets to establish the presence or absence of transgenic DNA. The LOD of transgenic DNS in milk was 7.5 μg/l. Feed and milk samples analysed at week 3 were negative. The TMR feed samples at weeks 4 and 12 were positive for CP4EPSPS soyabean meal DNA, but all milk samples were negative. The results showed that transgenic DNA could not be detected in milk from cows receiving upto 26.1% of their diet DM as herbicide (glyphosate)-tolerant soyabean meal.

The effect of crop maturity on the nutritional value of maize silage for lactating dairy cows. 2. Ruminal and post-ruminal digestion

To evaluate the effect of crop maturity on digestion of maize silage in the rumen and post-ruminal digestive tract, four multiparous Holstein-Friesian cows fitted with a simple cannula in the proximal duodenum and a rumen cannula were offered four diets in a 4 ✕ 4 Latin-square design. Forage maize (cv. Hudson) was harvested and ensiled at target dry matter (DM) contents of 230, 280, 330 and 380 g per kg fresh weight (FW) to provide a range of starch contents. The mean values for volatile-corrected DM (VCDM) and starch content of the four maize silages as given were 221, 277, 308 and 372 g/kg FW and 173, 257, 328 and 382 g/kg VCDM respectively. Grass silage (GS) containing 250 g VCDM per kg FW was produced from the primary growth of a perennial ryegrass sward. The diets were 8·7 kg DM per day of a dairy concentrate supplement with one of four forage treatments offered ad libitum. The forage treatments were a 3 : 1 DM ratio of maize silage with GS, designated as T23, T28, T33 and T38. Each period lasted 6 weeks with rumen and duodenal samples being taken over 3 days in week 4 and faeces being collected in respiration chambers over 6 days in either week 5 or 6. Milk yield tended to increase with advancing maturity (30·5, 31·8, 32·5 and 32·3 kg/day) but individual treatment differences were not significant. DM intake increased from 19·62 to 21·30 kg/day ( P P P P P

The effect of crop maturity on the nutritional value of maize silage for lactating dairy cows 1. Energy and nitrogen utilization.

Four multiparous Holstein-Friesian cows fitted with simple cannulas in the proximal duodenum and the rumen were offered four diets in a 4 ✕ 4 Latin-square design to evaluate the effect on energy and nitrogen balance of crop maturity of maize when offered as ensiled food with grass silage and a concentrate. Forage maize (cv. Hudson) was ensiled at target dry matter (DM) contents of 230, 280, 330 and 380 g per kg fresh weight (FW). The mean values for volatile corrected DM (VCDM) and starch content of the maize forages as given were 226, 278, 319 and 357 g/kg FW and 180, 263, 327 and 401 g/kg VCDM respectively. Grass silage (GS) containing 247 g VCDM per kg FW was produced from the primary growth of a perennial ryegrass sward. The diets comprised 8·7 kg DM concentrate per day with one of four forage treatments offered ad libitum, in a 3 : 1 DM ratio of maize silage with GS, designated T23, T28, T33 and T38. Each period was of 6 weeks with energy and nitrogen balances conducted in respiration chambers over 6 days in either week 5 or 6. There were no significant effects of maturity on DM intake. Changes in milk yield and composition were not significant but milk protein yield increased significantly ( P P P P P P P

A review of empirical and mechanistic models of lactational performance by the dairy cow

Abstract Current feeding systems for dairy cows are based principally on metabolisable energy and aim to meet calculated energy requirements. They do not predict milk composition or the response of the animal to changes in nutrient inputs and are thus inadequate in the current situation of production quotas and payments based on yield of milk constituents. Models which include the digestive and metabolic fate of individual nutrients, while providing as simple a representation as possible, therefore need to be considered. Models may be empirical, that is relate input to outputs without consideration of the intervening metabolism, or mechanistic, that is the response of the whole animal is simulated by the representation of individual tissues. These different approaches to modelling are considered, reviewing progress made to date, highlighting current inadequacies and discussing the future potential of these approaches. Empirical and mechanistic representations of the lactation curve, that is of the time course of lactation, are first considered, followed by empirical and mechanistic models of the response of the cow to dietary inputs. Finally future research needs are discussed in the light of the changed circumstances in the dairy industry.

Intake, live-weight gain and carcass characteristics of beef cattle given diets based on forage maize silage harvested at different stages of maturity

Advancing maturity of forage maize is associated with increases in the proportion of dry matter (DM) and starch, and decreases in the proportions of structural carbohydrates in the ensiled crop. This experiment investigated the effects of three maize silages of 291 (low), 339 (medium) and 393 (high) g DM per kg fresh weight on the performance of 48 Simmental. Holstein-Friesian cattle. Equal numbers of steers (mean start weight = 503 (s.d. 31.3) kg) and heifers (mean start weight = 378 (s.d. 11.2) kg) were offered individually isonitrogenous diets composed of the three silages plus a protein supplement with minerals once daily until slaughter at the target live weight of 575 and 475 kg for steers and heifers, respectively. Intake was reduced on the low diet (P 0.05) between diets. There were no differences in live-weight gain between treatments but differences (P < 0.05) in food conversion efficiency indicated relative gains of 115, 100 and 102 g gain per kg DM intake for diets low, medium and high, respectively. There were no differences between diets in carcass weights, fat score and overall conformation.

Milk production from grass silage diets: effects of high-protein concentrates for lactating heifers and cows on intake, milk production and milk nitrogen fractions

To examine the effects of increasing the crude protein (CP) content of concentrates at either equal concentrate intake (increasing CP intake) or at reducing concentrate intake (equal CP intake), 44 multiparous Holstein-Friesian cows were allocated to one of five treatments for weeks 4 to 18 of lactation. The treatments were 6 kg dry matter (DM) per day of concentrates containing nominally 200, 300 or 400 g CP per kg DM or 9 or 3 kg DM per day of concentrates containing 200 or 600 g CP per kg DM respectively. In addition 23 first-calf cows (heifers) were offered 5 kg DM per day of concentrates containing 200, 300 or 400 g CP per kg DM. All the animals were offered first-cut perennial ryegrass silage ad libitum . Increasing the concentrate CP content at equal intake caused only small and non-significant increases in silage intake by both heifers and cows. It significantly increased yields of milk and milk protein for both groups but whereas the cows responded to both increments of CP, the heifers only responded to the first. The concentrations of total protein, true protein, casein and non-protein nitrogen (NPN) in milk were significantly increased but the concentration of whey protein remained unchanged. Increasing CP concentration while the concentrate ration was reduced enhanced silage intake but had no significant effect on yields of milk or milk solids. The concentrations of total protein, true protein (non-significant), casein and NPN all increased but whey protein was unchanged. Overall the concentrations of casein and NPN were linearly related to the dietary CP concentration. With both concentrate strategies the proportion of true protein in total milk protein decreased and the proportion of NPN increased with increasing dietary CP concentration but the changes, though highly significant, were relatively small. It is concluded that the strategy of reducing the concentrate ration while maintaining concentrate CP intake causes only small reductions in milk solids production but it is dependent for success on supplies of high-quality grass silage to substitute for the concentrates.