High Breeding Index Research Articles

Evaluating enteric methane emissions within a herd of genetically divergent grazing dairy cows

Enteric methane (CH4) emissions of 3 genetic groups (GG) of dairy cows were recorded across the grazing season (early March to late October). The 3 GG were (1) high economic breeding index (EBI) Holstein-Friesian (HF) representative of the top 1% of dairy cows in Ireland at the time of the study (elite), (2) national average (NA) EBI, which were representative of the average HF dairy cow in Ireland, and (3) purebred Jersey (JE) cows. Enteric CH4 was recorded using GreenFeed technology. Seasonal variation in CH4 was observed, with the lowest daily CH4 emissions and CH4 expressed per unit of dry matter intake occurring in spring (253 g/d and 15.56 g/kg, respectively), intermediate in summer (303 g/d and 18.26 g/kg, respectively), and greatest in autumn (324 g/d and 19.80 g/kg, respectively). Seasonal variation was also observed in the proportion of gross energy intake converted to CH4 (Ym); in the spring the Ym was lowest at 0.046, increasing to 0.053 and 0.058 in the summer and autumn, respectively. There was no difference in daily CH4 between the elite and NA, whereas JE had lower CH4 emissions compared with the elite. When expressed per unit of milk solids (fat + protein yield; MS), the elite and JE produced 6.8% and 9.7% less CH4 per kilogram of MS, respectively, compared with NA. There was no difference between the GG for CH4 per unit of DMI or the Ym. This research emphasizes the variation in CH4 emissions across the grazing season and among cows of differing genetic merit for CH4 emission intensities but not for CH4 per unit of DMI or the Ym.

Assessment of mosquito larval habitats, species abundance and diversity in Azare, Katagum Local Government Area, Bauchi State, Nigeria

The study investigated the abundance and diversity of mosquito species larvae in different larval breeding habitats of Azare, Katagum L.G.A., Bauchi State, Nigeria. The selected habitats were surveyed weekly between August and October, 2021 across ten communities. A total of 2,320 mosquito larvae of different instars were collected and reared to adults in which 1,624 successfully emerged as adults comprising of three genera namely: Anopheles 464 (20%), Culex 928 (40.00%) and Aedes 232 (10%). A total of four (4) species were identified; two (2) of which were Anopheles spp. (An. gambiae and An. arabiensis), one (1) Culex spp. (Cx. quinquefasciatus), one (1) Aedes spp. (Ae. aegypti); while the numbers of unidentified individuals for Culex and Aedes genera down to species level were one (1) species for each respectively. The results of this study found high species abundance and relatively low diversity but a high larval breeding index. There was no significant difference (p > 0.05) in larval abundance among the three groups. Most interestingly, the study found out that mosquitoes’ larvae co-habit together in relation to the breeding habitats sampled across the study area. The results of this study signify high transmission risk of mosquitoes-borne diseases in the area. Thus, control interventions, to reduce malaria burdens and other arboviruses, in the city should be broadened to target the breeding sites of mosquitoes by implementing a larviciding strategy especially during the wet season is presumably the most cost-effective strategy to consider.

Greenhouse gas emissions and nitrogen efficiency of dairy cows of divergent economic breeding index under seasonal pasture-based management

Greenhouse gas (GHG) emissions and nitrogen (N) efficiencies were modeled for 2 genetic groups (GG) of Holstein-Friesian cows across 3 contrasting feeding treatments (FT). The 2 GG were (1) high economic breeding index (EBI) animals representative of the top 5% of cows nationally (elite) and (2) EBI representative of the national average (NA). The FT represented (1) generous feeding of pasture, (2) a slight restriction in pasture allowance, and (3) a high-concentrate feeding system with adequate pasture allowance. Greenhouse gas and N balance models were parameterized using outputs generated from the Moorepark Dairy Systems model, a stochastic budgetary simulation model, having integrated biological data pertaining to the 6 scenarios (2 GG × 3 FT) obtained from a 4-yr experiment conducted between 2013 and 2016. On a per hectare basis, total system GHG emissions were similar for both elite and NA across the 3 FT. Per unit of product, however, the elite group had 10% and 11% lower GHG emissions per kilogram of fat- and protein-corrected milk and per kilogram of milk solids (MSO; fat + protein kg), respectively, compared with the NA across the 3 FT. The FT incorporating high concentrate supplementation had greater absolute GHG emissions per hectare as well as GHG per kilogram of fat- and protein-corrected milk and MSO. The elite group had a slightly superior N use efficiency (N output/N input) and lower N surplus (N input - N output) compared with the NA group. The high concentrate FT had an inferior N use efficiency and a higher N surplus. The results of the current study demonstrate that breeding for increased EBI will lead to a general improvement in GHG emissions per unit of product as well as improved N efficiency. The results also illustrate that reducing concentrate supplementation will reduce GHG emissions, GHG emissions intensity, while improving N efficiency in the context of pasture-based dairy production.

IDENTIFICATION OF GRAIN PLANTS BY SELECTION INDICES

The highest selection index obtained from the genotypes of soybeans: UD0202557 – 0,21, UD0202566 – 0,21, UD0202468 – 0,21, UD0202529 – 0,21. It should be noted that these cultivars are different types in the parameters of ecological plasticity and stability. For varancau stability, all cultivars that were studied are stable, varansi stability maximum was close to zero. According to the results of variance analysis it was found that the formation of a selection index (weight of seeds/number of beans per plant) were more influenced by the year conditions, however, have a significant influence of varietal characteristics and interaction of varieties with haratine conditions years of research. The highest breeding index (seed weight per plant and number of seeds per plant) have provided varieties of soybean: UD0200773 – 0,14, UD0202201 – 0,14, UD0202566 – 0,14, UD0202468 – 0,14. Most of these genotypes belong to the highly plastic – UD0202201, UD0202566, UD0202468. Cultivars that have provided high breeding index (seed weight per plant and number of seeds per plant) was also characterized by high levels of agronomic stability of 99.9%. In addition, these cultivars had high homeostaticity and 1.4. At formation of indicators of the selection index (weight of seeds/number of seeds per plant) is more influenced by varietal characteristics, this is indicated by the results of mathematical processing of two-factor analysis of variance.The highest selection index weight of seeds/number of nodes on the plant were characterized by varieties of soybean : UD0202468 AND 0.43, UD0202557 AT 0.42, UD0202566 AT 0.42, UD0200773 – 0,41, UD0202201 – 0,41. These cultivars of soybean in response to the improvement of hydrothermal regime is treated as a highly plastic: UD0202201, UD0202557, as well as conservative. The highest rates of this selection index (number of seeds/number of productive nodes) obtained from the genotypes of soybeans: UD0202557 WAS 3.18, UD0202566 – 3,14, UD0202468 – 3.21 m. These cultivars for reaction to improve the hydrothermal regime relate to highly plastic (b1>1). The formation of this selection index is significantly influenced by the conditions of the year. Key words:cultivars of soybean, the parameters of adaptability and coefficient of plasticity, agronomic stability, varansi stability.

Factors affecting magnesium concentration from June to March in spring‐calving dairy cows

Abstract A total of 109 cows calving in July and August in a breed × stocking rate trial at Ruakura were blood‐sampled for plasma magnesium (Mg) on seven occasions from June 1990 to March 1991. The objectives were to monitor the effects of month, breed, stocking rate, age, calving day, and covariation with yield of milksolids on Mg concentration. The Friesian and Jersey cows were sired by high breeding index New Zealand Dairy Board bulls, and low and high stocking rates were 3.02 and 3.98 cows/ha respectively for Friesian and 3.57 and 4.53 cows/ha for Jersey. Mg supplementation was applied before calving using MgO on pasture, hay, or silage. Once‐daily drenching with 10 g Mg/cow (as MgCl2) was carried out after calving and continued until November, before the fourth monthly sample was collected. Monthly mean Mg concentrations were 0.87, 0.91, 1.12, 1.06, 0.98, 0.94, and 0.93 mM/1 in June, August, October, December, January, February, and March. There were significant effects of breed in August, October, and overall, with higher Mg concentrations recorded in Jerseys than Friesians. Over all samplings, stocking rate was significant (P < 0.05), with a 4% lower concentration at the high than low stocking rate. In the two months when age was significant (December and January), cows of 5 years and older had lower Mg concentrations than younger cows. Date of calving was not a significant effect. The between‐cow repeatability of Mg concentration from month to month was 0.31 ± 0.04. The regressions of Mg concentration on yields of milk or milksolids were significant for February and March samples, but the regressions only accounted for a small percentage of Mg variation. In conclusion, for four herds supplemented with Mg from pre‐calving until November, there were only small differences in Mg concentration across management groups or breeds, and associations with yield were of minor importance.

Pancreatic insulin responses to exogenous glucose in Friesian heifers of low or high genetic merit for milk-fat yield

AbstractTwo studies were conducted to examine the effects of selection for milk-fat yield on pancreatic responses to exogenous glucose, as measured by circulating insulin concentrations following an intravenous glucose load, in heifer calves. The first study involved 6-month-old Friesian heifers, eight each from the Massey University high breeding index (HBI) and low breeding index (LBI) lines. Average breeding indices (BI) for milk-fat yield of the calves based on ancestry BI were 136 (s.d. 2) and 112 (s.d. 2), respectively. Oestrous cycling of the heifers was controlled by intravaginal insertion of progesterone-impregnated controlled internal drug-releasing devices (CIDRs). Challenges of glucose (0, 75, 150 and 300 mg/kg live weight) and insulin (0, 0·1, 1, and 10 fig/kg live weight) were administered via indwelling jugular cannulas and were followed by serial blood sampling to measure responses. Plasma insulin concentrations immediately following the glucose challenge were significantly (P &lt; 0·05) greater in HBI than in LBI heifers, peak insulin concentrations (above baseline) in the HBI group being approximately twice those in the LBI group. Plasma glucose concentrations were marginally lower in HBI heifers, probably due to the secondary effect of the relatively greater hyperinsulinaemia in this group. Although the exogenous insulin challenge significantly reduced circulating glucose concentrations in all heifers, there was no difference between the lines in the magnitude of insulin-induced hypoglycaemia.The second study was designed to determine whether insulin responses to an exogenous glucose load were influenced by stage of the oestrous cycle in heifers of the two lines. In this study, eight yearling HBI heifers and eight LBI heifers (with BI of 135 (s.d. 4) and 111 (s.d. 1) respectively) were administered an intravenous glucose load (150 mg/kg live weight) on tivo occasions, the first being after 17 days of CIDR treatment (simulating the luteal phase of the oestrous cycle) and the second 46 h after withdrawal of the CIDRs (when the heifers were expected to be in oestrus). HBI heifers again showed significantly greater circulating insulin concentrations than LBI heifers following the glucose challenge but the magnitude of this effect was not influenced by time relative to CIDR withdrawal. It is concluded that heifers selected for high milk-fat yield have an increased pancreatic response to exogenous glucose which is apparently independent of the stage of the oestrous cycle. This difference may provide a useful means of identifying heifers of superior genetic merit for milk-fat production prior to their first lactation.

Plasma metabolite and hormone concentrations in Friesian calves of low or high genetic merit: effects of sex and age

AbstractThis study investigated the potential use of blood metabolite and hormone concentrations as genetic markers for milk fat production and their possible interactions with sex and age. Two groups of calves, one from the Massey University high breeding index (HBI) line of dairy cattle (seven males, eight females) and the other from the low breeding index (LBI) line (four males, 11 females), were studied at 3·5 months and 7 months of age. The average breeding indices (BI) of the calves based on ancestry BI were 138 (s.d. 4·4) and 111 (s.d. 2·3) respectively. Serial blood sampling regimens were conducted in relation to feeding (chaffed lucerne hay at 1·3 times maintenance energy requirement), during an intravenous urea load (120 mg/kg live weight) and during fasting (63 h) and refeeding. Urea spaces and fractional decay constants at each age were estimated by a single compartment distribution model based on plasma urea concentrations following the intravenous urea load.Plasma concentrations of urea, creatinine and non-esterified fatty acids (NEFA) were not significantly different between the lines in any of the periods examined and at either age. In contrast, plasma concentrations of glucose and insulin were greater in the HBI calves than in the LBI calves although these differences were restricted mainly to the period immediately after feeding. Urea space at 7 months of age was also greater in the HBI animals than in the LBI animals. Plasma concentrations of all hormones and metabolites except insulin were significantly influenced by sex and/or age.The study does not confirm previous findings that genetic merit for dairying is expressed in terms of plasma levels of urea and NEFA, particularly those during a fast. However, the results of the present study are consistent with previous observations of differences in glucose and insulin metabolism between the tivo Massey University genetic merit lines. These traits may therefore have potential as genetic markers for milk fat production.

Diurnal variation in plasma metabolite and hormone concentrations and response to metabolic challenges in high breeding index and low breeding index Friesian heifers fed at two allowances

Abstract Diurnal variation in blood metabolite and hormone concentrations and their responses to acute intravenous injections of glucose, insulin, glucagon, and adrenaline were examined in twelve 6-8-month-old Friesian heifers born to either high breeding index (HBI) or low breeding index (LBI) parents. Heifers were fed once daily at below (75%) and above ( 125%) their maintenance energy requirement (MER) in a single reversal trial to test the effects of selection line and its interaction with energy balance. The concentration of all the metabolites and hormones measured varied over the day and, when compared with heifers fed 125% MER, those fed 75% MER exhibited: increased plasma creatinine concentrations; a smaller increment in plasma urea concentration after feeding; greater plasma non-esterified fatty acid (NEFA) concentrations in the post-prandial period; and lower insulin concentrations during the 24-h sampling period. Basal concentrations of insulin, creatinine, growth hormone, and NEFA were not in...

Metabolic responses to exogenous bovine somatotropin in Friesian cows of low or high genetic merit

Basal hormone/metabolite concentrations and responses to intravenous challenges of glucose, insulin and epinephrine were examined in Friesian cows from selection lines of low or high genetic merit treated with recombinantly-derived bovine somatotropin (bST) or control formulation in a 2 × 2 factorial design. Cows from the low genetic merit (low breeding index, LBI) line had previously been shown to be more responsive to the galactopoietic effects of bST (50 mg/day) than those from the high breeding index (HBI) line. Despite this, comparisons of metabolic differences were not confounded by differences in energy balance because bST treatment had also caused an increase in voluntary intake of cut pasture. Circulating levels of somatotropin, insulin-like growth factor-I (IGF-I) and insulin were greater in bST-treated than control cows but neither bST treatment nor selection line influenced basal concentrations of glucose, non-esterified fatty acids (NEFA), β-hydroxybutyrate, urea or creatinine. Treatment with bST produced a small increase in sensitivity of cows to the lipolytic effects of epinephrine and this effect was similar in both selection lines. HBI cows had greater circulating insulin levels following the glucose challenge than LBI cows but bST treatment did not affect the insulin response to exogenous glucose. Whereas bST treatment retarded the glycogenolytic response to epinephrine and the clearance of blood glucose in response to insulin in LBI cows, it had no effect on epinephrine-stimulated glycogenolysis, and caused enhanced glucose clearance in response to insulin, in HBI cows. Results are consistent with bST altering the homeorhetic control of metabolism but do not adequately explain the greater responsiveness of LBI cows to the galactopoietic effects of bST.

Effects of exogenous bovine somatotropin on milk yield and pasture intake in dairy cows of low or high genetic merit

ABSTRACTThe effect of recombinantly derived bovine somatotropin (bST) treatment on milk production and pasture intake was examined in 16 New Zealand Friesian cows from low or high genetic merit (breeding index) selection lines. Recombinantly derived bST was administered by 2-weekly injection of a controlled release formulation for a period of 4 weeks (weeks 16 to 19 of lactation) at a dose rate equivalent to 50 mg/day. During this period the animals were housed for 18 days with food intake being measured over the last 8 days. Treatment with bST resulted in significantly higher yields of milk, fat and protein compared with the controls. Cows from the low breeding index (LBI) line were more responsive to exogenous bST than cows of the high breeding index (HBI) line in both milk and fat yield. Milk composition was not affected by bST treatment. There was a significant increase of proportionately 0·108 in intake of freshly cut pasture between bST-treated and untreated animals during days 16 to 23 of treatment. Thus, no significant difference in calculated energy balance was observed between the bSTtreated and untreated cows. This study indicates that the genetic background of cows may be an important determinant of their response to bST treatment and that such treatment rapidly alters voluntary intake in pasture-fed cows.

Plasma metabolite and hormone concentrations as predictors of dairy merit in young Friesian bulls: effect of metabolic challenges and fasting

AbstractResponses to metabolic challenges were measured in 8-month-old Friesian bull calves with a view to identifying possible predictors of genetic merit for milk fat production. Seven ‘high’ breeding index bulls (mean breeding index for milk fat = 128·9 (s.d. 4·8) percentage units) were compared with six ‘low’ breeding index bulls (mean 107·3 (s.d. 2·4) percentage units). Bulls were from two selection lines and breeding indices calculated as the average of parental breeding index values.Challenges involved intravenous injection of the following (dose rates per kg body weight): adrenalin (1 μg); glucose (0·17 g); glucagon (0·175 μg); insulin (0·01 mg); and arginine (40 mg). Blood samples were withdrawn prior to and after each challenge (two challenges daily). Bulls were then fasted for 3 days before being refed.Relative to the low breeding index bulls, those in the high breeding index group exhibited: (a) greater pancreatic sensitivity to circulating glucose as indicated by increased insulin concentrations following the glucose challenge; (b) more rapid clearance of glucose from plasma following the insulin challenge; (c) reduced sensitivity to the glycogenolytic/gluconeogenic effects of glucagon as indicated by lower blood glucose concentrations following intravenous injection of this hormone; (d) elevated plasma insulin and growth hormone concentrations during the fasting period; (e) elevated plasma concentrations of insulin, glucose and urea during refeeding; (f) no difference in responses to intravenous arginine or adrenalin, or in circulating concentrations of Insulin-like Growth Factor-1 or alkaline phosphatase. Results are consistent with previous observations that metabolic differences between cattle in the Massey University high and low breeding index lines are most evident in the metabolism of glucose and insulin. Metabolic challenges offer a potentially useful means of predicting genetic merit for milk fat production but the conditions under which repeatable differences between the lines can best be demonstrated are yet to be determined.

Plasma metabolite and hormone concentrations in Friesian calves differing in genetic potential for milkfat production

Abstract The effects of fasting, feeding, and an arginine infusion on plasma concentrations of glucose, insulin, and growth hormone (GH) were examined in 39 milk-fed Friesian calves born to either high breeding index (HBI) or low breeding index (LBI) parents. In Trial 1, 13 male and 11 female calves were used when they were 8 – 18 days old. Glucose and insulin concentrations in plasma were consistently higher in the HBI group than in the LBI group. Differences in glucose concentration between the BI groups were significant (P < 0.05) following an overnight fast. Differences in insulin concentration were significant both after the overnight fast and after feeding. GH concentrations were generally higher in HBI than LBI calves and the difference was significant (P < 0.05) following arginine infusion. In Trial 2, eight HBI and seven LBI bull calves were bled at 18 – 26 days old for 3 consecutive days. It was again observed that glucose concentrations were significantly higher in the HBI calves than in the LB...

Some milking characteristics of Jersey cows of differing breeding index

Abstract ‘Cups-on time’ (COT) for individual Jersey cows was measured using two techniques during six consecutive milkings in 2 consecutive weeks during peak lactation (October–November). Four groups of 15 animals included two groups with a high breeding index (HBI) of 127 and two groups with a low breeding index (LBI) of 101. HBI cows averaged 15.5 kg milk/day compared to 12.5 kg/day for the LBI cows. Morning (AM) milk weights for all groups were twice the afternoon (PM) milk weights at milking intervals of 16:8 h. The average COT at AM milkings was 7.6 min/cow compared to 5.7 min/cow at PM milkings. The average flow rate (AFR) at AM milkings was 1.33 kg/min for HBI cows and 1.13 kg/min for LBI cows. Comparable AFRs at PM milkings were 0.88 (HBI) and 0.75 kg/min (LBI). Differences related to BI in COT and AFR were not statistically significant, partly because of the large variation among individual cows within a BI group. This study showed that the increased production of Jersey cows resulting from the use of progeny tested HBI sires has not increased COT.

Blood metabolite responses to catecholamine injections in heifers of high or low genetic merit for milkfat production

Abstract Responses to acute intravenous injections of adrenalin and noradrenalin were examined in two groups of heifers (4 heifers/group) differing in predicted genetic merit by a mean of 33 breeding index units. A split-plot design was used in which the heifers were paired, one high breeding index and one low breeding index, for main plot comparisons between breeding index groups. Subplot treatments (four doses: 0, 0.25, 0.5, and 1 µg/kg bodyweight of noradrenalin; and four times of challenge: 1000 hand 1500 h on two consecutive days) were arranged in two 4 × 4 Latin Squares and applied to the four heifer pairs. The design was repeated on Days 3 and 4 using a second catecholamine, adrenalin. The concentrations of glucose and non-esterified fatty acids were measured in plasma collected at intervals (− 15, − 1, 5, 10, 15,20, 30, 45, 60, and 120 min) from treatment. Samples following the highest dose of each catecholamine were also analysed for insulin and 3-hydroxybutyrate. Glucose response to adrenalin in...

Performance of Friesian cows with high and low breeding indexes 2. Energy and nitrogen balance experiments with lactating and pregnant, non-lactating cows

ABSTRACTSix lactating Friesian cows (three high and three low breeding index cows) were subjected to a total of 28 complete energy and nitrogen balances during early and late lactation. In addition, 12 non-lactating Friesian cows (six high and six low breeding index cows) were offered individually pasture indoors for 62 days, beginning at approx. 180 days of pregnancy. Cows within each genotype were randomly allocated to feeding levels which were nominally equivalent to their requirements for maintenance or twice maintenance. Eight of the 12 cows (four high and four low breeding index) were each subjected to two energy balance periods at approx. 210 (period 1) and 230 (period 2) days of pregnancy.When offered pasture ad libitum during lactation, cows with high breeding indexes consumed significantly more gross energy per unit of metabolic live weight (P &lt; 0·05) than did cows with low breeding indexes, but the two genotypes did not differ in their ability to metabolize the gross energy of the food, or in the individual losses of energy in faeces, urine or methane.There were no significant differences between genotypes in their heat production at a common energy intake except during restricted feeding in early lactation when high breeding index cows produced less heat than did low breeding index cows (P &lt; 0·05). During lactation high breeding index cows retained a higher proportion of their total energy retention (milk + body tissue energy) as milk in late lactation (P &lt; 0·01) but not in early lactation.For non-lactating cows, both genotypes required similar amounts of metabolizable energy to maintain zero maternal body energy retention, 0·79 and 0·80 MJ/M0·75 for periods 1 and 2 respectively. The efficiency with which metabolizable energy was converted to net energy (kg) was similar for both genotypes at both stages of pregnancy, the mean value being 0·52. The metabolizable energy required to maintain body condition was estimated to be 0·78 and 0·71 MJ/M0·75 for high and low breeding index cows respectively. The metabolizable energy required in excess of maintenance to promote a gain of one unit of body condition was estimated to be 2290 MJ. This is equivalent to 27 MJ energy retained per kg live-weight gain.For lactating and non-lactating cows the differences between genotypes in their utilization of nitrogen were small and inconsistent.

Performance of Friesian cows with high and low breeding indexes 1. Stall feeding and grazing experiments and performance during the whole lactation

ABSTRACTThe performance of 38 Friesian cows with either high or low breeding indexes was measured during the whole lactation and in short-term experiments where the cows were individually given cut pasture in stalls, or grazed on pasture.Cows with high breeding indexes produced more milk fat than did cows with low breeding indexes in the short-term experiments, and during the whole lactation. There was close agreement between the expected differences (predicted from breeding indexes) and the measured differences in milk fat yield. When fresh cut pasture was given ad libitum in stalls the intake per cow was the same between genotypes. However, when intake was expressed per unit of metabolic weight, the mean pasture drymatter intake of the high breeding index cows was 1·05 of that of the low breeding index cows, but the difference was significant in only one of the four indoor feeding experiments.The difference between genotypes in size was not regarded as significant because the differences in mean live weight at calving (high breeding index – low breeding index) of the animals purchased in the 1st and 2nd years were –28 and 9 kg respectively. During the whole lactation, low breeding index cows gained significantly more live weight and lost significantly less body condition than did the high breeding index cows. No significant differences in live-weight and body-condition changes could be detected during the shorter periods (4 to 5 weeks) of the indoor feeding and grazing experiments.It can be calculated that the higher milk production of the high breeding index cows could be explained partly because they eat more (per unit metabolic live weight) and more importantly because they divert a higher proportion of the food they eat to milk production and a lower proportion to live-weight gain than do the low breeding index cows.

Plasma metabolite and hormone concentrations in Friesian cows of differing genetic merit measured at two feeding levels

ABSTRACTPhysiological differences between cows in hormone and metabolite concentrations were sought that may account for genetic differences in milk production.Two groups of New Zealand Friesian cows, differing in genetic merit for fat production (high breeding index (HBI) and low breeding index (LBI)) by approximately 23 breeding index units (20 kg fat on the United Kingdom improved contemporary comparison scale), were each divided into two further groups, one of which was given freshly cut pasture to appetite and in the other intake was restricted to 70% of appetite. Eighteen blood samples were collected over a 24-h period from each of 16 cows fitted with indwelling jugular catheters. Samples were analysed for growth hormone, insulin, free fatty acids and β-hydroxybutyrate. Mean concentration of insulin was significantly higher in the HBI underfed group than in any other group (P&lt; 0·01). Glucose concentration was significantly lower in the LBI group (P&lt; 0·05), whose intake was restricted. The concentration of (3-hydroxybutyrate was significantly higher in the cows whose intake was restricted (P&lt; 0·01) and the concentration fell markedly after feeding. Growth hormone concentrations were higher in the cows on restricted intake (P&lt; 0·05) and in HBI cows but the differences were not statistically significant.It was concluded that different patterns of blood metabolites and hormones are associated with cows that differ in genetic merit. Aspects of insulin and glucose metabolism, particularly at low planes of feeding, appear to offer most promise as indicators of high milk-solids production.

Evaluation of the use of chromic oxide to estimate the feed intake of dairy cows

Abstract In each of 3 trials, the digestible organic matter (DOM) intake of 32 cows was determined by direct measurement and by a chromic oxide technique. Each trial involved either 2 or 3 21-day periods during lactation. Half of the cows had high Breeding Index (BI) and half had low BI. Cows were individually housed and offered pasture either ad libitum or 75070 ad libitum. Dosing with chromic oxide (10g Cr203 in a gelatin capsule) and sampling of faeces from the rectum occurred twice daily. Organic matter (OM) digestibility of the feed was obtained by in vitro determination, and both actual and estimated intakes are expressed as kg DOM per cow per week. Breeding Index had no significant effect on the relationship between estimated and actual intake. The chromic oxide technique consistently overestimated actual intake, but there were significant differences between weeks within and between periods in extent of overestimation. Mean overestimation was 14%. The variation in intake between cows of similar BI was greater for the chromic oxide technique. This resulted in the chromic oxide technique being less sensitive in detection of real differences in intake between the BI groups. Of the 33 comparisons in food intake of the 2 BI groups, significant differences were found on 31 and 18 occasions with the direct measurement and chromic oxide techniques respectively.

Factors Influencing the Uneven Distribution of Aedes Aegypti in Texas Cities 1

SummaryThe prevalence of Aedes aegypti in early summer in Texas cities is very variable. Only in the Lower Rio Grande Valley is the winter climate mild enough to allow this mosquito to survive, without protected hold-over places, in sufficient numbers to produce a high incidence of breeding early in the season every year. In other cities early prevalence of breeding is associated with abundance of protected winter hold-over places, especially cisterns, fire-protection barrels in compresses and warehouses, or shallow wells. In cities having only a few such hold-over places, a high breeding index does not develop until late summer, and in many smaller cities such an index may not develop at all unless the mosquitoes are imported from elsewhere in automobiles or freight cars. In such cities the occurrence and prevalence of Aedes aegypti may vary from year to year depending on whether or not such an importation occurs early in the season. In coastal cities, alternation of cold and warm periods during the winter has a harmful effect on the survival of Aedes aegypti, and may be more important in holding the insect in check than the extremes of cold, or the total amount of cold weather.