A survey of the phosphorus and calcium contents of pastures and the serum inorganic phosphorus and calcium contents of cows on four Manawatu dairy farms

Serum inorganic phosphorus (Pi) and calcium (Ca) concentrations were assessed in 20 cows on each of four Manawatu factory supply dairy farms. Blood was taken from each cow before calving and at six-week intervals during lactation. Bleeding coincided with herd testing. Herds of Friesian or Friesian X cows and Jersey or Jersey X cows were compared on adjacent farms on a Central Yellow-brown Sand and on adjacent farms on a Peat Loam overlying a Central Yellow-brown Earth soil. Pasture mass and composition were estimated to grazing height in the next two paddocks to be grazed in the rotation. Mean serum Pi concentration was higher in cows on sandy soils (1.55 mmol Pi/l than in cows on the peat loam (1.34 mmol Pi/l (P<0.001). Concentrations were highest before calving (1.69 mmol Pi/l) but fell to low levels at peak lactation (1.17mmol Pi/l when 70% of cows were below the minima of the 'normal range', and during the drought (1.29 mmol Pi/l. Pasture phosphorus (P) concentrations were adequate to support cow nutrition for lactation (>0.33% DM, ad lib. feeding) until the summer drought when low herbage mass would have restricted milk production. Serum Ca was adequate for lactating cows and changed little between months or between cows (mean 2.12 mmol Ca/l). No metabolic disorders relating to mineral deficiencies were observed. It appears that serum Pi in a high proportion of cows falls below the normal range during peak lactation without cows displaying clinical deficiency symptoms or a depression in butterfat production.     

Phosphorus supplementation of lactating dairy cattle on a Northland farm

Forty-eight Friesian or Friesian-X factory supply dairy cows were divided into two groups. Group 1 received a supplement of sodiumtripolyphosphate (TPP, 25g P, 25g Na/cow/day), and group 2 a supplement of sodium chloride (25g Na/cow/day). Supplementation began at peak lactation, when the mean serum inorganic phosphorus (Pi) of all cows was 1.13 mmol/l. After four weeks, group 2 changed from NaCl to dicalcium phosphate supplementation (25g P/cow/day). Serum Pi and yields of milk, butterfat and protein were measured before, during and after supplementation. Pasture availability was assessed and P and Ca contents in pasture and the Pi content in milk were also determined. Supplementation raised serum Pi from 1.30 mmol/l (NaCI) to 1.42 mmol/l (TPP, P<0.05) but when dicalcium phosphate replaced NaCl the difference between groups disappeared (P>0.05). P supplementation had no effect on any milk parameter. Pre-grazing pasture mass above estimated grazing height averaged 2260 kg DM and contained >or=0.39 per cent P. It is concluded that a herd mean serum Pi concentration of around 1.2-1.3 mmol/l imposes no limitation to dairy production around the period of peak lactation of grazing dairy cattle.     

Phosphorus supplementation of lactating dairy cattle on a Northland farm

Abstract

Forty-eight Friesian or Friesian-X factory supply dairy cows were divided into two groups. Group 1 received a supplement of sodiumtripolyphosphate (TPP, 25g P, 25g Na/cow/day), and group 2 a supplement of sodium chloride (25g Na/cow/day). Supplementation began at peak lactation, when the mean serum inorganic phosphorus (Pi) of all cows was 1.13 mmol/l. After four weeks, group 2 changed from NaCl to dicalcium phosphate supplementation (25g P/cow/day). Serum Pi and yields of milk, butterfat and protein were measured before, during and after supplementation. Pasture availability was assessed and P and Ca contents in pasture and the Pi content in milk were also determined. Supplementation raised serum Pi from 1.30 mmol/l (NaCI) to 1.42 mmol/l (TPP, P<0.05) but when dicalcium phosphate replaced NaCl the difference between groups disappeared (P>0.05). P supplementation had no effect on any milk parameter. Pre-grazing pasture mass above estimated grazing height averaged 2260 kg DM and contained ?0.39 per cent P. It is concluded that a herd mean serum Pi concentration of around 1.2–1.3 mmol/l imposes no limitation to dairy production around the period of peak lactation of grazing dairy cattle.     

Effect of dietary phosphorus content on milk production and phosphorus excretion in dairy cows

Background

Phosphorus (P) supplementation is costly and can result in excess P excretion. This study investigated the effects of reducing dietary P on milk production and P excretion in dairy cows over a full lactation.

Method

Forty-five multiparous Holstein dairy cows were divided into 15 blocks according to expected calving date and previous milk yield, and assigned randomly to one of the three dietary treatments: 0.37, 0.47, and 0.57% P (DM basis); these P levels represent the NRC recommendations, Chinese recommendations, and the amount of dietary P commonly fed by Chinese dairy farmers, respectively. Average daily feed intake was calculated from monthly data on feed offered and refused. Milk yields of individual cows were recorded weekly, and milk samples were taken for analysis of protein, fat, solids-not-fat, lactose, and somatic cell count. Blood samples were collected on days −6, −3, 0, 3, 6 relative to calving, and then monthly throughout lactation, and analyzed for P and Ca concentrations. Spot samples of feces and urine were collected for 3 consecutive d during weeks 12, 24, and 36, and P concentrations were analyzed. Reproduction and health data were recorded.

Results

Dietary P did not affect dry matter intake or milk yield (P > 0.10). Milk fat content was slightly higher in cows fed 0.37% P than in cows fed 0.47% P (P = 0.05). Serum concentrations of P and Ca did not reflect dietary P content (P > 0.10). Fecal and urinary P both declined linearly (P < 0.05) as dietary P decreased from 0.57 to 0.37%. Fecal P content was 25% less when dietary P was 0.37% compared to 0.57%. Health events and reproductive performance were not associated with dietary P content (P > 0.05).

Conclusions

Lowering dietary P from 0.57 to 0.37% did not negatively affect milk production, but did significantly reduce P excretion into environment.     

A farming systems study of abortion in dairy cattle on the Atherton Tableland: 4. Pasture composition and plasma progesterone concentrations of pregnant cows in affected herds

To provide more evidence for an apparent association between immature, high protein pasture diets and abortion in dairy cows on the Atherton Tableland in tropical north Queensland, pastures and cows on 4 farms were sampled on 5 occasions during a 7-month period. Pasture samples were analysed for dry matter (DM), protein, nitrate and fibre content. Plasma progesterone concentrations were determined in 18 to 20 pregnant cows. Fifty-four pasture samples (38 grass and 16 legume) were analysed and the distribution for 3 DM ranges was: 10% to 14.9% - 20 samples, 15% to 19.9% - 27 samples and 20% to 24.9% - 7 samples, while the distribution for 4 protein ranges was: 15% to 19% - 5 samples, 20% to 24% - 20 samples, 25% to 29% - 21 samples and 30% to 34% - 8 samples. Both pasture protein and DM content fluctuated with time. Pasture nitrate was low and insignificant while fibre (cell wall) levels appeared to be satisfactory for ruminant nutrition. Significant differences occurred between the mean plasma progesterone levels on 3 of the 4 farms. Raised levels in pregnant cows suggested the possibility of increased progesterone production in response to a previous low progesterone crisis or, alternatively, a decreased metabolic clearance rate of progesterone in pregnant cows on a declining plane of nutrition towards the end of the summer wet season. Progesterone data were not available from cows which previously aborted.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nutrient balance in the diet of spring calving, pasture-fed dairy cows

AIMS: To report the nutrient composition of pastures fed to spring-calving dairy cows in the Manawatu region of New Zealand, and describe changes in the nutrient composition of these pastures over a 12-month period. Having done this we sought to: (1) compare the nutrient composition of the pasture offered with the nutrient requirements of spring-calving dairy cows; (2) identify periods when individual nutrient surpluses and deficits are likely; and, (3) identify nutrients that demonstrate a high level of variability between sampling occasions. METHODS: Seven farms took part in the study. Each farm was visited monthly from August 1996 to July 1997. Samples of pasture were taken at each visit and submitted for estimation of dry matter (DM), metabolisable energy (ME), crude protein (CP), non-structural carbohydrate (NSC), neutral detergent fibre (NDF), acid detergent fibre (ADF), calcium (Ca), phosphorus (P), magnesium (Mg), sodium (Na), potassium (K), chlorine (Cl), sulphur (S), iron (Fe), copper (Cu) and zinc (Zn), and dietary cation-anion differences (DCAD). RESULTS: Sampled pastures were characterised by low to marginal ME, NSC, Ca, Mg, and Zn concentrations when compared with recommended dietary nutrient concentrations for lactating and non-lactating dairy cattle in New Zealand. Analyses revealed relatively high CP, NDF and K concentrations, and DCAD. CONCLUSIONS: These analyses identify broad trends in the nutrient balance of a pasture-only feeding regime and provide a useful reference for planning feed strategies for spring-calving, pasture-fed dairy herds in this region. Recommended changes to on-farm practice should be made after considering the whole farm system, rather than being made solely on the basis of perceived deficiencies or excesses of individual nutrients.     

Does body size of dairy cows,at constant ratio of maintenance to production requirements,affect productivity in a pasture‐based production system?

This study compared productivity of dairy cows with different body weight (BW), but a constant ratio of maintenance to production requirements in their first lactation, in a pasture-based production system with spring calving. Two herds, Herd L (13 and 14 large cows in 2003 and 2004 respectively; average BW after calving, 721 kg) and Herd S (16 small cows in both years; 606 kg) [Correction added after online publication 14 January 2011: 16 small cows in both years; 621 kg was changed to 16 small cows in both years; 606 kg], all in their second or following lactations, were each allocated 6 ha of pasture and rotationally grazed on 10 parallel paddocks with equal herbage offer and nutritional values. Winter hay, harvested from the same pastures, was offered ad libitum in the indoor periods in a tied stall barn. Each herd received, per lactation and year, approximately 2000 kg dry matter (DM) of concentrates and of fodder beets, equally distributed to every individual. Indoors, the L-cows ingested more DM than the S-cows (18.7 vs. 16.3 kg DM/cow per day; p < 0.01), but DM intake per 100 kg of metabolic BW was similar (13.0 vs. 13.1 kg DM/cow per day). Estimates based on the n-alkane technique gave similar results on pasture (17.9 vs. 15.5 kg DM/cow per day; p < 0.001). Roughage intakes per 100 kg of metabolic BW, at 13.5 kg DM/cow per day, were similar. Mean annual yield of energy-corrected milk (ECM)/ha was slightly higher for the S-herd than the L-herd (13,026 vs. 12,284 kg) but was associated with a higher stocking rate (on average +20%) for the S-herd. Feed conversion efficiency (1.2 vs. 1.3 kg ECM/kg DM intake) and overall milk production efficiency (45.3 vs. 47.3 kg ECM/kg metabolic BW) were similar in L- and S-cows. Thus, both dairy cow types were equally efficient in utilising pasture-based forage.     

Associations between dairy herd management factors and bulk tank milk antibody levels against Ostertagia ostertagi

A cross-sectional questionnaire survey was performed on dairy herds in Flanders (Belgium) to detect management factors that are associated with an increased gastrointestinal parasite infection level of adult dairy cows. At the end of the grazing season, information concerning general herd factors, pasture management and anthelmintic treatment strategy was obtained from 956 herds. A bulk tank milk sample was obtained from 779 out of the 956 herds and the antibody levels (ODR) against Ostertagia ostertagi were determined. The associations between ODR and herd management factors were studied by two linear regression models. The first model evaluated the effect of general herd factors and the level of the cows' exposure to pasture. Large sized herds had significantly lower ODRs as compared to medium (P=0.001) or small sized herds (P=0.03). Herds with only dairy cows had lower ODRs than herds with both dairy and beef cows (P=0.02). An increased exposure to pasture of the cows was associated with higher ODRs (P<0.001). The second model was built to evaluate the effect of pasture management factors and anthelmintic treatment strategy. Later turn-out on pasture (P<0.001) and mowing (P=0.002) were both significantly associated with lower ODRs. Cows that had a restricted grazing time per day tended to have lower ODR than cows that grazed 24 h per day (P=0.07). An increased exposure to pasture of the heifers was significantly associated with higher ODRs (P=0.001). No associations were found between ODR and calf related management factors, anthelmintic treatment strategy, time of turn-in, rotational grazing type or stocking rate. Later turn-out on pasture, mowing and restricting the grazing time per day are factors that can be applied immediately on dairy farms to reduce economical losses due to gastrointestinal nematodes.     

Kikuyu over-sown with ryegrass and clover: dry matter production,botanical composition and nutritional value

The seasonality of growth and low nutritional value of kikuyu (Pennisetum clandestinum) pasture restrict milk production. The aim of the study was to determine the dry matter yield, botanical composition and nutritional value of irrigated kikuyu over-sown with annual ryegrass (Lolium multiflorum var. westerwoldicum), white clover (Trifolium repens) and red clover (T. pratense) or a mixture of perennial ryegrass (Lolium perenne) with white and red clovers under intensive grazing conditions with dairy cows. The incorporation of annual ryegrass, perennial clover or perennial ryegrass–clover into kikuyu pasture changed the seasonal fodder flow and increased the spring dry matter (DM) production. The over-sowing of kikuyu with annual ryegrass had no effect on the DM production of kikuyu during the summer and autumn. Kikuyu and kikuyu–ryegrass, fertilised with nitrogen fertiliser, had a higher DM production rate than kikuyu–clover pastures. Kikuyu–ryegrass pasture transformed from ryegrass-dominant in spring to kikuyu-dominant in summer and only kikuyu in autumn. This led to a decrease in metabolisable energy (ME) and increase in neutral detergent fibre (NDF) content of the pasture during spring, summer and autumn as kikuyu became more dominant. The clover content of kikuyu over-sown with clover decreased annually but was still higher than 30% at the end of two years after establishment. As the kikuyu content of the kikuyu–clover pastures increased, the seasonal growth rate changed from a low autumn growth (37.9 kg DM ha^?1 d^?1) in the first year to a higher autumn growth (48.5 kg DM ha^?1 d^?1) in the second year. The over-sowing of kikuyu with clover resulted in lower DM production and NDF values and higher crude protein (CP), ME and calcium (Ca) values. The lowest CP content in kikuyu–ryegrass pasture was during summer and autumn when kikuyu was dominant. The Ca content of the grass pastures (kikuyu and kikuyu–ryegrass) was low. The phosphorus (P) content of both the kikuyu–clover and grass pastures exceeded the requirement needed for dairy production (0.38%). The mean Ca:P ratio of the kikuyu–clover pasture meets the 1.6:1 ratio needed by dairy cows. The kikuyu and kikuyu–ryegrass pasture had a Ca:P ratio lower than 1:1 and Ca supplementation would be needed for dairy cows. The incorporation of annual ryegrass, perennial clover or perennial ryegrass–clover into kikuyu pasture improved the seasonal DM production and nutritional value of the pasture.     

泌乳奶牛采食、反刍、逍遥行为和日粮纤维性物质表观消化率对比分析

为了对比不同泌乳阶段奶牛的采食、反刍、逍遥行为和日粮营养物质表观消化率,选择体重、胎次相近的8头健康荷斯坦泌乳奶牛,其中,4头处于泌乳盛期(泌乳盛期组),4头处于泌乳后期(泌乳后期组),进行了采食行为观察和消化试验,两组奶牛预饲期20 d,正试期15 d。结果表明,泌乳盛期组奶牛每天的干物质采食量为21.2 kg,极显著高于泌乳后期组的14.1 kg(P<0.01),但两组奶牛的采食时间和采食次数无显著差异(P>0.05),泌乳盛期组奶牛每千克DM采食的时间也极显著低于泌乳后期组奶牛(P<0.01);一昼夜总反刍时间泌乳盛期组奶牛极显著低于泌乳后期组(P<0.01),每千克DMI需反刍时间泌乳盛期组奶牛极显著低于泌乳后期组(P<0.01)。泌乳盛期组奶牛躺卧、走动和站立时间与泌乳后期组奶牛相比无显著差异(P>0.05)。泌乳盛期组奶牛日粮中NDF和ADF的表观消化率极显著低于泌乳后期组(P<0.01),两组奶牛NDF的表观消化率分别为55.8%、67.8%,ADF的表观消化率分别为44.2%、60.7%。     

Prevalence of ketonemia and associations with herd size, lactation stage, parity, and postparturient diseases in Jordanian dairy cattle.

The prevalence of bovine ketonemia among 1155 dairy cows in various stages of lactation and parity on 25 Jordanian dairy herds was studied. The cross-sectional study was conducted during the spring of 1992. Serum concentration of beta-hydroxybutyrate (BHB) <0.9 mmol/l, between 0.9 and 1.7 mmol/l, and >1.7 mmol/l were considered to indicate normal, mild and severe ketonemia, respectively. The point prevalences of mild and severe ketonemia were 22% and 3.8%, respectively. The prevalence of ketonemia decreased with increasing herd size. Associations between the prevalence of ketonemia and parity, stage of lactation, metritis, somatic-cell count (SCC) and serum cholesterol levels were not significant (p > 0.05).     

Effect of water‐soluble carbohydrate content in orchardgrass pasture on grazing time and rumen fermentation in dairy cows

Two experiments were conducted to clarify the effect of water‐soluble carbohydrate (WSC) content in orchardgrass pasture on the diurnal distribution of grazing time. Six ruminally cannulated, non‐lactating dairy cows were grazed on either of two pastures with different orchardgrass cultivars containing low WSC (LWSC; cultivar: ‘Hokkai 28’) or high WSC (HWSC; cultivar: ‘Harunemidori’). The cows were grazed in morning and evening sessions in experiment 1, whereas the cows were grazed throughout the day in experiment 2. In experiment 1, grazing time of the cows on HWSC was longer than that of the cows on LWSC (P < 0.01). This difference was larger in the morning session than in the evening session (pasture × grazing session: P < 0.05). Effects on herbage intake were similar to those on grazing time. In experiment 2, daily total grazing time was longer for the cows on HWSC than for those on LWSC (P < 0.05). The cows on HWSC spent a longer time grazing than those on LWSC in the morning between 03.00 and 09.00 hours (P < 0.01). The results indicated that prolonged grazing time in the period between dawn and early morning could increase daily herbage intake in cows grazed on pastures of orchardgrass cultivars with high‐WSC content.     

Influence of low phosphorus intake during early lactation on apparent digestibility of phosphorus and bone metabolism in dairy cows

In this study, the effects of reducing the dietary phosphorus (P) supply during the first 4 months of lactation on P balance and bone metabolism were investigated in dairy cows during a full lactation, including the dry period. Twenty-two multiparous cows of the Swedish Red and White Breed were included in the experiment. Eleven cows received a dietary P concentration of 0.43% of DM during the whole lactation (NP), and 11 cows received a dietary P concentration of 0.32% of DM during the first 4 months of lactation, followed by 0.43% of DM during the rest of lactation (LP). Total collection of faeces was carried out during five different stages of lactation, for 5 consecutive days at each occasion. The dynamics of bone metabolism was investigated by monitoring one bone-formation marker, identifying osteocalcin (OC), and one bone-resorption marker identifying C-telopeptide fragments of collagen type I (CTx) in blood plasma. At the two first collection periods, 3–7 and 11–15 weeks after parturition, the apparent digestibility of P was higher in the LP cows (52%) than in the NP cows (42%). During the following collection periods, no difference in the apparent digestibility could be noted between the two groups of cows. Phosphorus retention did not differ between treatments at any collection period. The highest retention was observed during late lactation and during the dry period. The profiles of the bone metabolism markers indicated a net resorption of bone during early lactation, but there were no differences in marker concentrations between the groups during early lactation, indicating that the LP diet did not induce a further elevated net bone resorption.     

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.     

Loss of reserves of Cu in liver when Cu supplements are withdrawn from dairy herds in the Waikato region

Abstract

AIM: To monitor the consequences of withdrawing mineral Cu supplements from two dairy herds with initially high concentrations of Cu in liver.

METHODS: Two herds were selected from dairy farms in the Waikato region of New Zealand that participated in an earlier survey of Cu supplementation practices and Cu status of dairy cows. The herds were fed pasture, grass and maize silage, plus palm kernel expeller (PKE) containing 25–30 mg Cu/kg dry matter (DM) fed at 2–4 kg/cow/day. No mineral Cu supplements were supplied from January 2009. Pasture samples were collected for mineral analysis in September 2008 and April 2009. Concentration of Cu in liver biopsies from the same 9–10 cows per herd was measured on three occasions between April 2009 and May 2010.

RESULTS: Pastures on both farms contained 10 mg Cu/kg DM, 0.1–0.5 mg Mo/kg DM and 3.5–4.0 g S/kg DM. The initial herd mean concentrations of Cu in liver were 1,500 (SD 590) and 1,250 (SD 640) μmol Cu/kg fresh tissue. In the absence of mineral Cu supplements, those mean concentrations decreased over 12 months to 705 (SD 370) and 1,120 (SD 560) μmol Cu/kg fresh tissue, respectively. For cows in the first herd, the rate of depletion of liver Cu reserves was influenced by initial concentration of Cu, such that high concentration led to faster loss according to first-order kinetics.

CONCLUSIONS: Mineral Cu supplementation was not necessary over 12 months for two dairy herds with mean concentrations of Cu in liver >1,250 μmol Cu/kg fresh tissue, grazing pastures containing 10 mg Cu/kg DM and concentrations of Mo <1 mg/kg DM. The quantity and particularly the duration of feeding PKE appeared to be a factor in whether or not the herd lost substantial reserves of Cu in liver during the year. However, the Cu status of both herds in this study was more than adequate to support late pregnancy and mating.

CLINICAL REVELANCE: Copper status of the herd should be monitored and on-farm management of Cu nutrition should take into account all sources contributing to daily intake of Cu. Where Cu supplementation has been excessive and there is risk of chronic Cu toxicity, mineral Cu supplements may be withdrawn for a period commensurate with the expected rate of liver Cu depletion.     

An assessment of the copper status of dairy herds in the Waikato, Taranaki and Northland in spring and the effects of daily supplementation with copper sulphate

The copper status of dairy herds in the Waikato, Taranaki and Northland regions between 1 August and 30 September was assessed by copper determinations made on composite sera from ten cows in each herd. Comparisons were made between two major groups categorised as as received and supplemented. In the latter, the cows received 2.0-6.0 g/day of copper sulphate orally from late gestation to the end of lactation. Mean copper values were determined from pastures in Taranaki and Northland and from pastures from three soil types in the Waikato. The lowest were in Northland (134.3 micromol/kg) and the highest in Taranaki (173.3 micromol/kg). Calculated dietary available copper levels showed the lowest were from pastures grown on organic soils in the Waikato. These soils also had high molybdenum levels. Serum copper values as received were lowest in Northland (7.30 micromol/l), and were marginal for both Taranaki (9.91 micromol/l) and the Waikato (9.93 micromol/l). The levels in supplemented herds were considerably higher, i.e. from the Waikato 11.7 micromol/l and from Taranaki 11.5 micromol/l. When liver and serum copper levels from paired samples were compared there was a reasonable correlation (r = 0.64) but the standard deviation approximated the mean liver copper level, i.e. 155 +/- 141 micromol/l.     

Effect of grazing pasture with a low selenium content on the concentrations of triiodothyronine and thyroxine in serum, and GSH-Px activity in erythrocytes in cows in Chile

AIM: To determine the effect of grazing pasture that had a low selenium (Se) concentration on serum concentrations of triiodothyronine (T3) and thyroxine (T4), and erythrocyte glutathione peroxidase (GSH-Px) activity in dairy cows. METHODS: Forty pregnant Friesian cows were grazed on pasture that contained 0.03-0.04 ppm Se on a dry matter (DM) basis. Two months before parturition, 20 cows were randomly selected and treated with 1 mg Se/kg bodyweight subcutaneously, as barium selenate (Group Se-S). The other group (Se-D) was not supplemented. Blood samples were taken before supplementation (-60 days) and 30, 60, 90, 180 and 270 days after parturition, for determination of concentrations of T3 and T4 in serum, and GSH-Px activity in erythrocytes. RESULTS: Erythrocyte GSH-Px activity in the Se-D group was <60 U/g haemoglobin (Hb) throughout the experiment. Supplementation increased (p<0.05) activities to >130 U/g Hb throughout lactation. Mean serum concentrations of T4 in Se-D and Se-S cows increased from 23.7 (SEM 0.7) and 23.4 (SEM 0.8) nmol/L, respectively, in the prepartum period to 69.6 (SEM 0.1) and 67.6 (SEM 0.2) nmol/L, respectively, at 180 days of lactation (p<0.01), and no effect of Se supplementation was evident. Serum concentrations of T3 in Se-D cows decreased (p<0.05) from 1.6 (SEM 0.1) nmol/L prepartum to 1.0 (SEM 0.2) nmol/L at the beginning of lactation, and remained lower (p<0.05) than those in the Se-S cows which did not decrease after calving and ranged from 1.9 (SEM 0.1) to 2.4 (SEM 0.2) nmol/L throughout lactation. CONCLUSIONS: Serum T3 concentrations decreased during early lactation in unsupplemented cows grazing pastures low in Se (0.03-0.04 ppm) and both serum T3 and erythrocyte GSHPx activities were consistently lower throughout lactation compared with Se-supplemented cows. Se supplementation had no effect on serum T4 concentrations.     

Osteomalacia as a result of phosphorus deficiency in beef cattle grazing subtropical native pastures in Uruguay

We investigated 2 outbreaks of osteomalacia as a result of phosphorus (P) deficiency in herds of lactating beef cows grazing subtropical native pastures in Uruguay. Cows exhibited pica, difficulty to stand and walk, rib fractures, and body weight loss even with adequate forage availability. Osteopenia and severe osteomalacia were observed on gross and histologic examination. The concentrations of bicarbonate-extractable P in soil (4.0, 4.1 mg P/kg), total P in pasture (0.9, 1.1 g P/kg), inorganic P in serum (1.0, 0.71 mmol P/L), and P in bone (73 mg P/mL) were all low. Although injectable and mineral salt supplements provided additional P in both outbreaks, these supplementary amounts were insufficient to prevent P deficiency. The P ingested by the cows from the pasture and supplements would have provided 20–55% of their daily P requirements of ~21 g P/d. Osteomalacia occurred in cattle at the 2 ranches as a result of severe P deficiency in the soil and forage, and inadequate P supplementation. Following diagnosis, control of P deficiency in beef cattle requires estimation of the amount of pasture P ingested and provision of sufficient additional supplementary P to meet the animals’ requirements.     

Bulk milk urea concentrations and their relationship with cow fertility in grazing dairy herds in southern Chile

Milk urea determination is being used as a broad indicator of protein/energy imbalance in dairy herds. The main purpose of this study was to compare blood and bulk milk urea values in grazing herds, to evaluate their seasonal variation under South Chilean conditions, and to examine their potential relationships with herd fertility. The association between herd blood urea concentration (mean of seven lactating cows) and bulk milk urea concentration (tank containing milk from the previous 24 h) was determined in 21 diary herds. Reference values, seasonal and herd variance, and the frequency of herds with values outside a range of 2.5 to 7.3 mmol/l were determined in bulk milk samples obtained monthly for a period of one year from 82 suppliers at two creameries located in southern Chile. Finally, bulk milk urea was measured every two weeks in samples from 24 herds, and the first service conception rate (FSCR) from 2153 dairy cows was determined. Mean bulk urea concentration was highly correlated with mean herd blood urea concentration (r = 0.95; p < 0.01). Mean urea concentration in the bulk milk samples obtained during one year from 82 herds was 4.9 +/- 1.2 mmol/l, with a range of 1.5 to 11.6 mmol/l. The highest values were found during spring and the lowest values during the summer. There was a high seasonal variation (CV = 13-47%) and between-herd variation (CV = 20-31%). Out of a total of 984 samples, 5.4% had urea values > 7.3 mmol/l and 3.8% had values < 2.5 mmol/l. Of the 82 herds, 27% had values outside the reference interval (2.5-7.3 mmol/l) on two or more occasions. FSCR was lower in herds when the bulk milk urea was > 7.3 mmol/l (50.7%) than in cows, where the urea concentration was < 5.0 mmol/l (73.8%) at the time of insemination. The study concluded that bulk milk urea concentrations provided information similar to herd blood urea concentrations in local grazing dairy herds. There was a high frequency of herds with abnormal values, with large variations between herds and between seasons. Increased milk urea concentrations during spring were associated with lower conception rates.     

Some effects of feeding pasture silage as a supplement to pasture on reproductive performance in lactating dairy cows

Supplementation of a ryegrass/white clover pasture diet with pasture silage is a common management practice in New Zealand dairy herds. The effect of this supplementation on reproductive performance has not been investigated. Five herds of 20 cows were formed before calving commenced on 1 June 1992. From 5 August to 4 September, two of these herds were fed 5 kg/cow/day of pasture silage in addition to the ryegrass/white clover pasture offered to all herds. Pasture silage supplementation did not alter the intervals from calving to first ovulation, first oestrus, or to conception. However, it reduced the first service conception rate (37.5% v. 53.3%; difference +/- sed = 15.8 +/- 10.0%, for pasture and silage and pasture only cows, respectively). A positive effect on reproductive performance of pasture silage supplementation was not demonstrated in this trial.