Effect of duration and level of supplementation of diets of lactating dairy cows with selenized yeast on selenium concentrations in milk and blood after the withdrawal of supplementation.

Cows' milk containing elevated concentrations of Se provides a rich nutritional source of this essential element for meeting daily nutritional requirements or providing health benefits in humans with low immune function or at risk of cancer. An experiment involving either 2 or 6 wk of dietary supplementation with Se yeast (with the yeast supplying about 30, 40, and 60 mg of Se/d for cows supplemented for 2 wk, and about 20, 30, 40, and 60 mg of Se/d for cows supplemented for 6 wk), and 21 wk of monitoring of Se status after the withdrawal of supplementation, was undertaken between September 2008 and April 2009 using 35 multiparous Holstein-Friesian cows. Using milk and blood Se concentrations as surrogates, the research examined the time taken for Se build-up in tissue due to supplementation of lactating dairy cows with Se yeast to dissipate back to normal levels. At the end of Se supplementation, a significant relationship was found between milk Se concentration and Se intake, whereby milk Se concentration had increased by 4.5 µg of Se/kg of milk for each mg of Se eaten per day, but no effect of duration of supplementation on this relationship was observed. At the same time, both Se intake and duration of supplementation affected blood Se concentration; it increased by 3.6 µg of Se/kg of blood for each mg of Se eaten per day, and was 86 µg of Se/kg higher after 6 wk compared with 2 wk of supplementation. After the withdrawal of Se supplementation, milk Se concentrations responded quickly to the change in the quantity of Se consumed, and again, duration of supplementation had no effect on the response, but any effect that Se intake had on milk Se had completely dissipated by 4 wk. In contrast to milk, blood Se concentrations continued to be affected by both amount and duration of Se supplementation for at least 4 mo after the withdrawal of supplementation, although by 5 mo the effects of the previous supplementation treatments had virtually disappeared. The slow decline in blood Se concentrations after the withdrawal of supplementation would most likely be due to the protracted clearance of Se from the various tissues that had accumulated Se during supplementation and the rate of erythrocyte turnover. When undertaking an on-farm Se enhancement program to generate milk for the manufacture of Se-enriched milk products, post-supplementation milk Se concentrations are unlikely to create any problems at the milk factory beyond 4 wk, but the high residual blood/tissue Se concentrations that take considerably more time to dissipate may provide the potential for possible unintended consequences at the food chain/farm environment level.

Selenium levels in cows fed pasture and concentrates or a total mixed ration and supplemented with selenized yeast to produce milk with supra-nutritional selenium concentrations.

Seventy multiparous Holstein-Friesian cows were fed different amounts of pasture and concentrates, or a total mixed ration (TMR), for 42 d in mid-lactation to test the hypothesis that the concentration of Se in milk would depend on the amount of Se consumed, when the Se is primarily organic in nature, regardless of the diet of the cows. Of the 70 cows, 60 grazed irrigated perennial pasture at daily allowances of either 20 or 40 kg of dry matter (DM)/cow. These cows received 1 of 3 amounts of concentrates, either 1, 3, or 6 kg of DM/cow per day of pellets, and at each level of concentrate feeding, the pellets were formulated to provide 1 of 2 quantities of Se from Se yeast, either about 16 or 32 mg of Se/d. The other 10 cows were included in 2 additional treatments where a TMR diet was supplemented with 1 kg of DM/d of pellets formulated to include 1 of the 2 quantities of supplemental Se. Total Se intakes ranged from 14.5 to 35.9 mg/d, and of this, the Se-enriched pellets provided 93, 91, and 72% of the Se for cows allocated 20 and 40 kg of pasture DM/d or the TMR, respectively. No effects of the amount of Se consumed on any milk production variable, or on somatic cell count, body weight, and body condition score, for either the pasture-fed or TMR-fed cows were found. Milk Se concentrations responded quickly to the commencement of Se supplementation, reaching 89% of steady state levels at d 5. When milk Se concentrations were at steady state (d 12 to 40), each 1mg of Se eaten increased the Se concentration of milk by 5.0 µg/kg (R(2)=0.97), and this response did not seem to be affected by the diet of the cows or their milk production. The concentration of Se in whole blood was more variable than that in milk, and took much longer to respond to change in Se status, but it was not affected by diet at any time either. For the on-farm production of Se-enriched milk, it is important to be able to predict milk Se concentration from Se input. In our study, type of diet did not affect this relationship.

Output of selenium in milk, urine, and feces is proportional to selenium intake in dairy cows fed a total mixed ration supplemented with selenium yeast.

Fifteen rumen fistulated Holstein cows in late lactation and fed a total mixed ration offered ad libitum were supplemented with Se yeast to provide 0, 11, 20, 30, or 42 mg of supplemental Se/day to test the hypothesis that amounts of Se secreted in milk, excreted in urine and feces, and apparently retained in tissues would increase in direct proportion to Se intake. One-half of the yeast supplement was placed directly into the rumen through the fistula of each cow just before milking in the morning and again in the evening, and estimates of average daily excretion of Se were made using total collections of urine and feces from 25 to 31 d after treatments commenced. Amounts of Se secreted daily in milk and apparently retained in tissues increased linearly with average daily intake of Se. The amount of Se excreted in feces and total excretion of Se in urine plus feces increased curvilinearly with Se intake, such that proportionately less Se was excreted as the amount of Se fed increased. On average, total Se excretion accounted for 66%, Se secretion in milk accounted for 17%, and Se apparently retained in tissues accounted for 17% of total Se intake by cows. Thus, in herds fed large amounts of Se yeast, most of the Se will be excreted and retained on-farm. High concentrations of Se will be found where urine and feces accumulate (e.g., yards and effluent ponds), and effluent management practices must be tailored to avoid environmental issues.

Increasing amounts of crushed wheat fed with pasture hay reduced dietary fiber digestibility in lactating dairy cows.

Sixteen cows in mid-lactation (milk yield of 23.8 +/- 2.3 kg/d) were individually fed diets consisting of chopped perennial ryegrass hay, offered at 3 kg of dry matter (DM)/100 kg of body weight (BW), fed either alone or supplemented with amounts of crushed wheat ranging from 0.4 to 1.6 kg of DM/100 kg of BW (increasing at nominal intervals of 0.4 kg of DM/100 kg of BW; 5 nominal treatments in total). Three cows were allocated to each treatment except the mid-range wheat treatment, which had 4 cows. Results were analyzed by regression because the intake of the wheat by cows within treatments varied. The hay was used to reflect the characteristics of summer pastures in southeastern Australia. Feed intake and fecal output were measured to determine digestion coefficients, feeds were incubated in nylon bags in the rumen, and rumen variables were monitored. Estimates of metabolizable energy (ME) of the hay from in vivo or in vitro digestibility were also compared. The digestibility of neutral detergent fiber (NDF) was depressed linearly as the amount of crushed wheat consumed increased to 36% of DM intake. The extent to which negative associative effects on NDF digestion were associated with the hay could not be determined, as it was not possible to distinguish between the NDF from hay and that from wheat. However, acid detergent fiber (ADF) digestion also declined, suggesting that most of the response lay with the hay because ADF was negligible in the wheat. Most data indicated that effects of proportion of wheat in the diet on the utilization of consumed nutrients were small. Despite substitution of wheat for hay reducing the forage intake of cows, there was a positive linear effect on marginal milk responses (1.3 kg of energy-corrected milk/kg of DM wheat). Mean rumen fluid pH declined as the proportion of wheat in the diet increased. The lowest pH for any individual cow during a 24-h period was 5.4, and the amount of time that rumen fluid pH was <6.0 ranged from 0 to 14 h depending on the amount of wheat consumed. It was concluded that these perturbations of the rumen environment were probably sufficient to result in negative associative effects. In addition, estimates of the ME content of the hay were higher when calculated from in vitro compared with in vivo digestibility, which has implications when estimating the amount of feed required for production.

Increasing selenium concentration in milk: effects of amount of selenium from yeast and cereal grain supplements.

Two experiments were conducted to establish responses in milk Se concentrations in grazing dairy cows to different amounts of dietary Se yeast, and to determine the effects of the Se concentration of the basal diet. The hypothesis tested was that the response in milk, blood, and tissue Se concentrations to supplemental Se would not be affected by whether the Se was from the basal diet or from Se yeast. In addition, by conducting a similar experiment in either early (spring; experiment 1) or late (autumn; experiment 2) lactation, we hypothesized that different Se input-output relationships would result. Both 6-wk experiments involved 60 multiparous Holstein-Friesian cows, all of which had calved in spring. They were allocated to 1 of 10 dietary Se treatments that included 2 types of crushed triticale grain (low Se, approximately 165 microg of Se/kg of DM; or high Se, approximately 580 microg/kg of DM) fed at 4 kg of DM/d, and 1 kg of DM/d of pellets formulated to carry 5 quantities of Se yeast (0, 4, 8, 12, or 16 mg of Se). Daily total Se intakes ranged from <2 to >18 mg/cow in both experiments. Milk Se concentrations plateaued after 15 and 7 d of supplementation in experiments 1 and 2, respectively, and then remained at plateau concentrations. Average milk Se concentrations for the plateau period increased as the amount of Se yeast increased, and low- and high-Se grain treatments were different at all quantities of Se yeast, although there was a tendency for this difference to diminish at the greatest concentrations of yeast. There were significant positive, linear relationships between Se intake and the concentrations of Se in milk, which were not affected by the source of Se, and the relationships were similar for both experiments. Therefore, the output of Se in milk in experiment 1 was greater than that in experiment 2 because the milk yield of the cows in early lactation was greater. The estimated proportions of Se partitioned to destinations other than milk and feces increased with the amount of Se in the diet and were greater in experiment 2 than in experiment 1, a result that was supported by Se concentrations in whole blood and plasma and in semitendinosus muscle tissue. If high-Se products are to be produced for human nutrition, it is important to be able to develop feeding systems that produce milk with consistent and predictable Se concentrations so that products can consistently meet specifications. The results indicate that this objective is achievable.

Acute post-parturient haemoglobinuria in dairy cows and phosphorus status.

During the conduct of an experiment designed to examine the nutritional management of dairy cows in late pregnancy, four cows out of 72 suffered from acute haemoglobinuria two to four weeks after calving. Thirty-six thin and 36 fat cows were individually fed one of three diets based on a total mixed ration with different energy or protein concentrations during the last 3 to 4 weeks before expected calving date. After calving, cows grazed pasture and were offered 6 kg dry matter of pelleted concentrates daily. The P concentrations of the feeds offered suggested that the cows' diets were marginally deficient in P relative to requirements. Plasma P concentrations were significantly (P < 0.05) lower in fat cows than in thin cows during the first 6 weeks of lactation (0.87 versus 1.12 mmol/L), but precalving diet had no effect (P > 0.05). Concentrations of plasma inorganic P of the four fat cows that developed acute haemoglobinuria were less than 0.3 mmol/L. However, plasma P concentrations in another 12 cows, none of which displayed overt symptoms, declined to similar levels. It appeared that inadequate dietary P may have predisposed cows to acute haemoglobinuria, but the precipitating cause was not readily obvious.

Relationships among international body condition scoring systems.

Scoring body condition and assessing changes in the body condition of dairy cattle have become strategic tools in both farm management and research. Consequently, body condition score (BCS) is being researched extensively throughout the world. However, international sharing, comparing, and use of data generated are limited because different BCS systems exist. In the United States and Ireland a 5-point BCS system is used for dairy cows, whereas Australia and New Zealand use 8- and 10-point scales, respectively. The New Zealand 10-point scale was compared with the scoring systems in the United States, Ireland, and Australia by trained assessors. Cows were assessed visually in the United States and Australia, and in Ireland, cows were assessed by palpating key areas of the cow's body (n = 154, 110, and 120, respectively). Data were analyzed by regression. Significant positive linear relationships were found between the New Zealand 10-point scale and the other scoring systems: US 5-point scale, r(2) = 0.54; Irish 5-point scale, r(2) = 0.72; and Australian 8-point scale, r(2) = 0.61. Those relationships must be interpreted cautiously because respective BCS within a given country were by just one experienced evaluator in each country in comparison to a separate evaluator scoring all cows in all counties using the New Zealand 10-point scale. Also, few very thin or very fat cows limit evaluation across extremes of BCS. However, differences between systems were not accurately predicted by simple mathematical calculations. The relationship may be closer for New Zealand and Ireland (r(2) = 0.72) because both of those scoring systems include palpation of individual body parts, whereas visual evaluation is done in Australia and the United States. The current study is the first to examine relationships among differing BCS systems. These results may be useful for comparing/extrapolating research findings from different countries.