Mature Cows Research Articles

Multi-species Grazing for Control of Gastrointestinal Nematodes – a Review

Abstract Multi-species grazing, alternate grazing of cattle with sheep or goats, offers benefits to gastrointestinal nematode (GIN) control as GIN species differ between hosts. In the Southeastern United States, common GIN species of cattle include Cooperia spp., Ostertagia ostertagi, Haemonchus spp., whereas species of sheep and goats are Haemonchus contortus, Teladorsagia circumcincta, Trichostrongylus spp., Cooperia curticei, and Oesophagostomum spp. Anthelmintic resistance is widely prevalent in small ruminants, and is an increasing problem in cattle, but remains less prevalent. Thus, it is recommended to farmers to use a multi-faceted approach of GIN control, including multi-species grazing. Because management differs between cattle and small ruminants in regard to copper tolerance in minerals, predator control and fencing, alternate grazing of species has most commonly been used. Other considerations include age or susceptibility to GIN, as young calves may be vulnerable to GIN, but mature cows often have negligible GIN infection. Similarly, weanling lambs and kids are susceptible, and depending on breed, adults range from highly resistant to susceptible. Research indicates that GIN burden of more resistant animals is less influenced by multi-species grazing, and highly susceptible animals will likely need additional measures of control. The more resistant species used in the multi-species grazing may lend more control to the more susceptible. Some research showed reductions in O. ostertagi, but not C. oncophora in cattle during extended grazing of cattle and sheep, and reductions of H. contortus and T. colubriformis in sheep. However, other research reported similar worm burdens. Weight gains were improved in lambs grazed alternately with cattle in some studies, and most studies showed little benefit to cattle. Little has been published on alternate grazing with cattle and goats. The complex interactions, larger plot sizes needed, and time required to complete experiments limits published studies of this important management scheme.

The Influence of Diet Type on Ranking for Feed Intake in Angus Cows

Abstract The objective of this study was to determine the effect of diet type on feed intake in mature Angus cows. Forty-eight gestating Angus cows (708 ± 52 kg; 7 ± 0.75 years old) were assigned to one of four drylot pens based on their genomic score for residual feed intake (“High” RFI, 7.3 ± 0.5, “Low” RFI, 5.5 ± 0.7). Each pen contained an automatic waterer as well as four GrowSafe individual feed intake units. During the first period, two of the four pens were assigned to a processed hay diet (10.0% CP, 1.98 Mcal ME/kg DM) while the other two pens consumed a mixed ration consisting of 43.0% hay, 33.0% corn, 13.0% soybean hulls, and 11.0% liquid supplement, DM basis (11.7% CP, DM basis and 2.43 Mcal ME/kg DM). Following a 14-day adaptation period, feed intake was recorded for 45 days. Subsequently, diet type was switched and followed by 14 days of adaptation to the new diet and 45 days of feed intake measurement. Data were analyzed as a crossover study using the GLIMMIX procedure in SAS v9.4. Pearson correlation coefficients were determined between phenotypic traits and genomic score. Feed intake was highly correlated (r = 0.75) among the two diet types. In comparison, average daily gain (ADG) was negatively correlated (r = -0.37) among the two diet types. No differences were observed in DMI or performance for cows ranked “high” or “low” based on genomic score. More research is required to determine if selection for increased weight gain when consuming a high-quality mixed ration could be detrimental to cattle performance consuming moderate to low-quality forage.

Relationship Between Gas Emissions and Dry Matter Intake in Mature Angus Cows

Abstract The objective of this study was to examine the effects of diet quality on greenhouse gas emissions and dry matter intake (DMI). We used 42 mature, gestating Angus cows (600±69 kg; and BSC 5.3±1.1) with a wide range in DMI EPD (-1.36 to 2.29). Cows were randomly assigned to 2 diet sequences forage-concentrate (FC) or concentrate-forage(CF) determined by the diet they consumed in each period (forage or concentrate). The cows were adapted to the diet and the SmartFeed individual intake units for 14 d followed by 45 d of intake data collection for each period. Body weight was recorded on consecutive weigh days at the beginning and end of each period and then once every two wk for the duration of a period. Cows were exposed to the GreenFeed Emission Monitoring (GEM) system for no less than 9 d during each period. The GEM system was used to measure emissions of carbon dioxide (CO2) and methane (CH4). Only cows with a minimum of 20 total >3-m visits to the GEM were included in the data set. Data were analyzed in a crossover design using GLIMMIX in SASv.9.4. Within the CF sequence there was a significant, positive correlation between TMR DMI and CH4 (r=0.81) and TMR DMI and CO2 (r=0.69), however, gas emissions during the second period on the hay diet were not correlated with hay intake. There was a significant, positive correlation between hay DMI and CO2 (r=0.76) and hay DMI and CH4 (r=0.74) when cows first consumed forage (FC). In comparison to the CF sequence, cows on the FC sequence showed a positive correlation between CO2 and TMR DMI during the second period. There was also a significant positive correlation between hay and TMR DMI when assessed across (r=0.43) or within sequence (FC r=0.41, CF r=0.47).

235 Resource Use for Beef Cattle in the North Central Great Plains

Abstract The sustainability of the beef industry has become a point of national interest, particularly the investment of land and water resources. Our objective was to estimate how much land and irrigation water are required to maintain a simulated Angus cow-calf operation in the North Central Great Plains (NCGP) for an average year. A stochastic model was used, which enabled consideration of biological variation. The model computed 100 iterations of a 24-year timeframe (1995–2018). The simulated herd had 100 breeding females with replacement heifers being retained annually. The nutrients required to maintain a body condition score 5 for each individual animal, adjusting for temperature and physiological state, were calculated. A stocking rate of 3.3 hectares (ha) per cow-calf pair and mature cow weight of 600 kg was set, which is representative of the NCGP. Replacement heifers were assumed to be 65% of mature cow weight and allotted 1.22 ha. Bred heifers were assumed to be 85% of mature cow weight and allotted 1.81 ha. The herd was assumed to be grazing from May 1 to October 31. A supplemented ration of 60% alfalfa and 40% corn was provided if an individual’s nutritional needs were not met. Animals were assumed to be delivered a base ration from November 1 to April 30, which consisted of 73% alfalfa, 19% wheat straw, and 8% corn. The amount of irrigation necessary to grow feed was determined by estimating evapotranspiration of each crop then subtracting the amount of precipitation during the growing season. Average crop yield was determined using county level data from the UDSA NASS to estimate how much land would be needed for feed production. Sustaining a 100 head cow-calf herd in the NCGP for an average year requires 103.5 million liters for irrigation, 1288.5 ha for crop production, 357 ha grazing land.

Prediction of genetic merit for live weight and body condition score in dairy cows using routinely available linear type and carcass data

Accurate estimates of genetic merit for both live weight and body condition score (BCS) could be useful additions to both national- and herd-breeding programs. Although recording live weight and BCS is not technologically arduous, data available for use in routine genetic evaluations are generally lacking. The objective of the present study was to explore the usefulness of routinely recorded data, namely linear type traits (which also included BCS but only assessed visually) and carcass traits in the pursuit of genetic evaluations for both live weight and BCS in dairy cows. The data consisted of on-farm records of live weight and BCS (assessed using both visual and tactile cues) from 33,242 dairy cows in 201 commercial Irish herds. These data were complemented with information on 6 body-related linear type traits (i.e., stature, angularity, chest width, body depth, BCS, and rump width) and 3 cull cow carcass measures (i.e., carcass weight, conformation, and fat cover) on a selection of these animals plus close relatives. (Co)variance components were estimated using animal linear mixed models. The genetic correlation between the type traits stature, angularity, body depth, chest width, rump width, and visually-assessed BCS with live weight was 0.68, -0.28, 0.43, 0.64, 0.61, and 0.44, respectively. The genetic correlation between angularity and BCS measured on farm (based on both visual and tactile appraisal) was -0.79; the genetic and phenotypic correlation between BCS assessed visually as part of the linear assessment with BCS assessed by producers using both tactile and visual cues was 0.90 and 0.27, respectively. The genetic (phenotypic) correlation between cull cow carcass weight and live weight was 0.81 (0.21), and the genetic (phenotypic) correlation between cull cow carcass fat cover and BCS assessed on live cows was 0.44 (0.12). Estimated breeding values (EBV) for live weight and BCS in a validation population of cows were generated using a multitrait evaluation with observations for just the type traits, just the carcass traits, and both the type traits and carcass traits; the EBV were compared with the respective live weight and BCS phenotypic observations. The regression of phenotypic live weight on its EBV from the multitrait evaluations was 1.00 (i.e., the expectation) when the EBV was generated using just linear type trait data, but less than 1 (0.83) when using just carcass data. However, the regression changed across parities and stages of lactation. The partial correlation (after adjusting for contemporary group, parity by stage of lactation, heterosis, and recombination loss) between phenotypic live weight and EBV for live weight estimated using the 3 different scenarios (i.e., type only, carcass only, type plus carcass) ranged from 0.38 to 0.43. Although the prediction of phenotypic BCS from its respective EBV was relatively good when using just the linear type trait data (regression coefficient of 0.83 with a partial correlation of 0.22), the predictive ability of BCS EBV based on just carcass data was poor and should not be used. Overall, linear type trait data are a useful source of information to predict live weight and BCS with minimal additional predictive value from also including carcass data. Nonetheless, in the absence of linear type trait data, information on carcass traits can be useful in predicting genetic merit for mature cow live weight. Prediction of cow BCS from cow carcass data is not recommended.

Comparative evaluation of selections groups for milking of full-age cows of various breeds

An assessment of the cow population based on exterior and productive characteristics in the formation of production groups identified by the level of milk yield was carried out. It is established that the selection parameters for the yield of milk in the breeding group of Mature cows of Simmental breed in Novosibirsk region for black-motley breed on 15% exceeds the requirements of the standard, red steppe -17.9, Simmental Khakassia - 23.5 %. The analysis of interbreeding differences by breeding groups shows that animals of the black-and-white breed significantly outperform their peers of other breeds in terms of chest width behind the shoulder blades, chest girth, milk yield and milk production index. Animals of the red steppe breed have superiority in live weight, width in makloks, oblique length of the trunk, oblique length of the back, fat content of milk, milk fat. Simmental cows bred in the Novosibirsk region surpass their peers in height at the withers, and simmentals of Khakassia are the leaders in height at the rump, chest depth, waist circumference, and exterior assessment. The assessment of the division of animals of the evaluated breeds into breeding groups by milk yield allows us to note that the leadership of the black-and-white breed is not so obvious among plentiful individuals. Cows of breeding groups of red steppe and Simmental breeds have the same productivity with black-and-white milk yield and milk yield index, and red steppe cows surpass their peers in milkfat content and milk fat. The selection of groups by milk yield showed the consolidation of the black-and-white breed by productive and exterior characteristics. The red steppe and Simmental breeds have a high potential for improvement. their breeding groups closely approach the analogues of the black-and-white breed in terms of milk production.

Genetic parameter estimations and genomic insights for teat and udder structure in young and mature Canadian Angus cows.

Poor teat and udder structure, frequently associated with older cows, impact cow production and health as well as calf morbidity and mortality. However, producer culling, for reasons including age, production, feed availability, and beef markets, creates a bias in teat (TS) and udder scores (US) assessed and submitted to the Canadian Angus Association for genetic evaluations toward improved mammary structure. In addition, due to the infancy of the reporting program, repeated scores are rare. Prior to the adoption of genetic evaluations for TS and US in Canadian Angus cattle, it is imperative to verify that TS and US from young cows are the same traits as TS and US estimated on mature cows. Genetic parameters for TS and US from all cows (n = 4,192) and then from young cows (parities 1 and 2) and from mature cows (parity ≥ 4) were estimated using a single-trait animal model. Genetic correlations for the traits between the two cow age groups were estimated using a two-trait animal model. Estimates of heritability (posterior SD [PSD]) were 0.32 (0.07) and 0.45 (0.07) for young TS and US and 0.27 (0.07) and 0.31 (0.07) for mature TS and US, respectively. Genetic correlation (PSD) between the young and mature traits was 0.87 (0.13) for TS and 0.40 (0.17) for US. Genome-wide association studies were used to further explore the genetic and biological commonalities and differences between the two groups. Although there were no genes in common for the two USs, 12 genes overlapped for TS in the two cow age groups. Interestingly, there were also 23 genes in common between TS and US in mature cows. Based on these findings, it is recommended that producers collect TS and US on their cow herd annually.

Comparison of Genetic Merit for Weight and Meat Traits between the Polled and Horned Cattle in Multiple Beef Breeds.

Simple SummaryBeef production has expanded worldwide through cattle adaptation to diverse environmental and husbandry conditions. The beef industry faces societal challenges from animal welfare perspectives, including dehorning and disbudding, which are common farm practices to limit animal and handler injuries by the horned cattle. Most cattle breeds were originally horned, and reluctance to poll breeding existed because of perceived negative correlations between polledness and production. In Australia, population trends indicate a recent rise to above 50% of poll types in six breeds (Charolais, Hereford, Limousin, Simmental, Shorthorn, and Droughtmaster), and two breeds with lower but increasing rates of polledness (Brahman and Santa Gertrudis). Overall, recently estimated breeding values of 12 investigated production traits have not shown consistently negative trends within and across breeds. Thus, polledness should not be considered as detrimental. Cautious breeding plans are warranted to avoid inbreeding depression in breeds with lower poll frequency. These findings should support the augmented poll breeding across the beef industry.Breeding for polled animals is deemed the most practical solution to eradicate horns naturally and circumvent management costs and risks on health and welfare. However, there has been a historical reluctance by some farmers to select polled animals due to perceived lower productivity of their calves. This study has compared estimated breeding values (EBVs) between horned and polled animals (N = 2,466,785) for 12 production and carcass traits to assess historical (before 2000) and recent (2000–2018) genetic implications of poll breeding. Older generations of the polled animals in most breeds had significantly lower (Bonferroni-corrected p = 0.05) genetic merits for live (birth to maturity) and carcass weights, milk, meat quality, and fat content traits. Substantial gains of genetic potential were achieved during 2000 to 2018 in each breed, such that polled animals have significantly improved for the majority of traits studied. Generally, polled cohorts showed advantageous EBVs for live and carcass weights irrespective of the lower birth weights in some breeds. While Polled Brahman showed inferior production parameters, the poll genetics’ effect size (d) and correlation (r) were very small on recent birth weight (d = −0.30, r = −0.08), 200 days (−0.19, −0.05), 400 days (−0.06, −0.02), 600 days (−0.05, −0.01), mature cow live weight (−0.08, −0.02), and carcass weight (−0.19, −0.05). In conclusion, although there is some evidence that historical selection for polled breeding animals may have reduced productivity, there is strong evidence that more recent selection for polled genotypes in the breeds studied has not resulted in any adverse effects on genetic merit.

Effect of late-gestation heat stress in nulliparous heifers on postnatal growth, passive transfer of immunoglobulin G, and thermoregulation of their calves

Youngstock such as nulliparous pregnant dairy heifers are not typically considered for active cooling, as they are thought to be more heat tolerant than mature cows. Recently, the benefits of heat stress abatement in pregnant heifers were studied, but the effect of in utero hyperthermia on the calf is still unknown. Herein, we aimed to investigate the effects of late-gestation heat stress in nulliparous heifers on the growth, immune, and thermoregulatory responses of their calves. Pregnant nulliparous dams were randomly selected for either active cooling (CL; fans and soakers; n = 15) or heat stress (HT; n = 16) 60 d before expected calving. After birth, respiration rate, rectal temperature, skin temperature, and sweating rate were obtained from their heifer calves at 24 h and on d 14, 28, 42, and 56. Blood samples and body weights were both collected for measurement of total protein and hematocrit and calculation of average daily gains, respectively. Gestation length was shorter in HT heifers (272 vs. 276 ± 1.28 d) relative to CL heifers. Birth weights, weaning weights, body weights up to d 56, and average daily gain from birth to weaning were not different between in utero HT (IUHT; n = 13) and in utero CL (IUCL; n = 12) calves. Apparent efficiency of absorption of immunoglobulin G tended to be lower in IUHT calves (26.3 vs. 42.7 ± 9.0%), and serum IgG concentrations from birth to d 56 were significantly lower in IUHT calves relative to IUCL calves (22.0 vs. 32.4 ± 4.47 g/L). Postnatal respiration rate, rectal temperature, sweating rate, total protein, and hematocrit were not different between in utero treatments. There was a tendency for IUHT calves to have lower skin temperature at 24 h (34.9 vs. 36.9 ± 1.05°C), and skin temperature tended to be elevated in IUHT calves at d 56 (29.6 vs. 27.9 ± 1.05°C). In summary, the lack of heat stress abatement during late gestation reduces gestation length of nulliparous heifers. Additionally, providing active cooling to nulliparous heifers during the prepartum period confers immune benefits to their offspring, although it does not translate to growth improvements.

Can Nitrogen Excretion of Dairy Cows Be Reduced by Genetic Selection for Low Milk Urea Nitrogen Concentration?

Simple SummaryNew Zealand dairy cows predominantly feed on pasture with protein to energy ratios well in excess of requirements and consequently their urine has a substantially greater concentration of nitrogen compared to cows fed indoors on total mixed rations. The nitrogen excreted directly onto land decompose into nitrous oxide and ammonium, causing global warming and freshwater pollution, respectively. One of the strategies to reduce the environmental contamination is genetic selection for reduced nitrogen excretion. The nitrogen excreted in urine is an expensive trait to measure in cows grazed outdoors. One possible approach to reduce the concentration of nitrogen excreted in urine is by selection for reduced urea nitrogen concentration in milk, which is readily measurable. The primary objective of this study was to quantify the likely correlated responses for milk production and liveweight traits in a selection index including breeding values for concentration of milk urea nitrogen with different relative emphasis in order to evaluate the usefulness of milk urea nitrogen for the purpose of reducing nitrogen excretion. Although a per cow reduction in urinary nitrogen excretion was predicted through selection in this study, the reduction of excretion is negligible at the whole farm level due to the influence of stocking rate, measured as the number of cows grazed per hectare, on the per hectare nitrogen excretion. Therefore, selection for low concentration of milk urea nitrogen is unlikely to be effective in reducing nitrogen excretion of dairy cows in New Zealand.The objectives of this study were two-fold. Firstly, to estimate the likely correlated responses in milk urea nitrogen (MUN) concentration, lactation yields of milk (MY), fat (FY) and crude protein (CPY) and mature cow liveweight (LWT) under three selection scenarios which varied in relative emphasis for MUN; 0% relative emphasis (MUN0%: equivalent to current New Zealand breeding worth index), and sign of the economic value; 20% relative emphasis positive selection (MUN+20%), and 20% relative emphasis negative selection (MUN−20%). Secondly, to estimate for these three scenarios the likely change in urinary nitrogen (UN) excretion under pasture based grazing conditions. The predicted genetic responses per cow per year for the current index were 16.4 kg MY, 2.0 kg FY, 1.4 kg CPY, −0.4 kg LWT and −0.05 mg/dL MUN. Positive selection on MUN in the index resulted in annual responses of 23.7 kg MY, 2.0 kg FY, 1.4 kg CPY, 0.6 kg LWT and 0.10 mg/dL MUN, while negative selection on MUN in the index resulted in annual responses of 5.4 kg MY, 1.6 kg FY, 1.0 kg CPY, −1.1 kg LWT and −0.17 mg/dL MUN. The MUN−20% reduced both MUN and cow productivity, whereas the MUN+20% increased MUN, milk production and LWT per cow. Per cow dry matter intake (DMI) was increased in all three scenarios as milk production increased compared to base year, therefore stocking rate (SR) was adjusted to control pasture cover. Paradoxically, ten years of selection with SR adjusted to maintain annual feed demand under the MUN+20% actually reduced per ha UN excretion by 3.54 kg, along with increases of 63 kg MY, 26 kg FY and 16 kg CPY compared to the base year. Ten years of selection on the MUN0% index generated a greater reductions of 10.45 kg UN and 30 kg MY, and increases of 32 kg FY and 21 kg CPY per ha, whereas the MUN−20% index reduced 14.06 kg UN and 136 kg MY with increases of 32 kg FY and 18 kg CPY compared to base year. All three scenarios increased partitioning of nitrogen excreted as feces. The selection index that excluded MUN was economically beneficial in the current economic circumstances over selection indices including MUN regardless of whether selection was either for or against MUN. There was no substantial benefit from an environmental point of view from including MUN in the Breeding Worth index, because N leaching is more a function of SR rather than of individual cow UN excretion. This study demonstrates that attention needs to be paid to the whole system consequences of selection for environmental outcomes in pastoral grazing circumstances.

Lameness in dairy heifers: a narrative review of control strategies

Lameness is a prevalent condition in mature dairy cows, but the common underlying diseases — sole bruising-sole ulcers, white line lesions and digital dermatitis — invariably arise from management factors in first lactation or rearing. The published evidence would indicate once infected by the Treponemes causing digital dermatitis, heifers retain these bacteria in the skin despite apparent clinical resolution, meaning the emphasis of control should be placed on minimising risk of early life exposure, largely through biocontainment, foot cleaning and foot disinfection. For sole bruising and sole ulcers, there has been a major switch from the acidosis and laminitis-base models of disease, to a biomechanical pathogenesis for claw horn lesions. This has focused attention on the development and preservation of the digital cushion, with the emphasis on preventive strategies combined with early intervention involving anti-inflammatory drugs among other things. This article reviews the evidence-based underpinning the rationale that heifers should be the focus of foot health control, a message that can be challenging to convey when the perceived problem invariably sits with how to deal with chronic, end-stage lesions.

Influence of the age of cows on the dynamics of dairy efficiency depending on a breeding line

The article suggests that one of the most widespread dairy breeds in the world is the Holstein breed; and the black-mottled breed in the Russian Federation. This breed has been improving during the past four decades by interbreeding it with the best one, the Holstein breed. A large set of the Holsteinized black-mottled livestock of the high thoroughbred cows of the Holstein breed has been produced. The aim of the work is to study the effect of age on the dynamics of dairy efficiency of the Holsteinized cows depending on the breeding line. At present, the dairy herd of the farm actually consists of cows of three breeding lines, Reflection Sovering 198998, Vis Back Ideal 1013415, Montvik Chieftain 95679. The rest breeds are not developing due to the absence of breeding valuable breeding bulls. It was found that the Reflection Sovering breeding line 198998 has that the highest milk yield during the sixth lactation, and then there is a decrease in milk yield. The article considers that the milk yield changes with age, starting from the first lactation, increasing during the second lactation and then it is gradually decreasing in productivity to the fifth one. The regularity of the increase in milk yield of mature cows during the third and fourth lactation is not confirmed of the dairy cows of this breeding line. It can be explained by the intensity of herb replacement, when it accumulates a significant amount of nutrients in the body. That is why, they can be used during the first and the second lactations without restoring nutrients in further. Dairy cows of the Vis Back Ideal 1013415 breeding line have a gradual increase in milk yield, starting from the first to the fourth lactation, by 52, 292, 300 kg or by 0.5; 2.8% and 2.8%, respectively. Further, there is a decrease in dairy efficiency. At reaching physiological maturity they have a natural increase in dairy efficiency. The same tendency is observed with cows of the Montvik Chieftein 95679 breeding line.

Economic and useful traits of cows of different ages

Intensive use of highly productive animals has revealed new problems associated with reducing the duration of productive use of animals and reducing their reproductive abilities, which lead to a decrease in the number of young animals for rearing and fattening for beef. Therefore, the study of the infl uence of age on the productive traits of cows is relevant and has practical signifi cance. The purpose of the work was to evaluate cows for economically useful traits depending on the age of the animals. It has been found that the milk yield for lactation increases with age in cows. If from fi rst-calf heifers has been received 5163,8±212,3 kg of milk, then 6106,5±201,7 and 6846,8±231,7 from cows of the third and fourth lactation, respectively, this was more by 942,7 kg or 18,2 % and 1683,8 kg or 32,6 %. Milk yield increases gradually from lactation to lactation with increasing age of cows and thus confi rms the association of improving the productive traits of animals with the laws of development, i.e. the onset of their physiological maturity. It has been revealed that the farm does not have optimal conditions for the full manifestation of the genetic potential of productivity, and therefore cows of the third and fourth lactation have lower milk yields than possible. So, the estimated milk yield of fi rstcalf heifers to mature cows practically corresponds to the milk yield that was received from cows after IV lactation. The diff erence between groups of cows in the content of individual components of milk was insignifi cant, although there is a positive trend to reduce the content of protein and casein with increasing age of cows. Cows bred on the farm have high indicators of reproductive ability. So, they have a short period of open day from 26,6±0,61 days (II lactation) to 43,7±1,11 days (III lactation), the optimal pregnancy period and calving interval (less than a calendar year). The level of profi tability of milk production increases with increasing milk yields, which increase with age.

OVARIAN STATUS OF NON-GRAVID SLAUGHTERED ZEBU COWS IN ZARIA: RELATIONSHIP WITH AGE, SEASON AND CARCASS WEIGHT

OF 3,900 non-gravid zebu ovaries examined at 3 Zaria slaughter houses, 2,652 (68%) were active, Ovarian activity was highest during the rainy season and anestrus highest during the dry season (P < 0.01). Anestrus non-gravid cows and empty cows with active ovaries had the lowest (135+41 kg) and the highest (170 +43 kg) carcass weight respectively. Aged anestrus empty COWS had the lowest carcass weight (127+28 kg) and mature empty cows with active ovaries had the highest (180 +47 kg). The incidence of anestrus increased with age. The magnitude of slaughtering of young and mature empty cows with active ovaries was discussed and it was recommended that rectal examination be done before culling animals in order to reduce this major source of loss of reproductively active cows.

Simulating Beef Cattle Herd Productivity with Varying Cow Liveweight and Fixed Feed Supply

The liveweight of New Zealand beef cows has increased in recent decades due to selection for higher growth rates. Published data suggest that the efficiency of beef cow production decreases with increasing cow liveweight. Changes in beef herd size, feed demand, production, and cash operating surplus (COS) were simulated with average mature cow liveweight varied to 450, 500, 550, and 600 kg. With total annual beef feed demand fixed at the same level, in all scenarios cow numbers and numbers of weaned calves decreased with increasing cow liveweight. When the model was run with consistent efficiency of calf production across the mature cow liveweights (scenario A), heavier cows were more profitable. However, using published efficiency data (scenarios B and C), herds of heavier cows were less profitable. The likely most realistic scenario for New Zealand hill country farms (scenario B) had COS decrease from New Zealand Dollars (NZD) 456/ha with a herd of 450 kg cows to NZD 424/ha with 600 kg cows. Reductions in COS were relatively small, which may not deter farmers from breeding heavier cows for higher calf growth rates. However, the results of this analysis combined with indirect potential economic impacts suggest that the heaviest cows may not be optimal for New Zealand hill country conditions.

EVALUATION OF THE REPRODUCTIVE PROBLEMS OF FRIESIANS, BUNAJI AND CROSSED COWS IN A SUBTROPICAL ENVIRONMENT

Herd health fertility records of 248 cows comprising 103 Friesians, 84 Bunaji and 61 Crossbreeds in Vom from 1992-1999 were utilized to study the incidence of reproductive problems. The overall incidence of various reproductive problems was 54.4% and this was more frequent (P<0.001) in crossbred cows (72.6%) than in Friesians, (59.9%) and in Bunaji (32.7%). Second Calvers (67.1%) were more susceptible (P<0.01) to reproductive problems than heifers (56.0%) and mature cows (45.3%). The incidence of still birth (8.10%) and relative infertility (8.2%), were influenced by genotype (P<0.05); similarly genotypic differences (P<0.001) were observed in the incidence of retained placenta (7.4%). Abortion (5.6%), dystocia (12.2%) and repeat breeding (12.5%) were uniformly distributed among genotypes. Parity of dams had marked influence (P<0.001) on dystocia, still birth and retained placenta. Significant differences (P<0.0l) were also observed on the incidence of relative infertility, but the rate of dystocia (P<0.01), abortion and repeat breeding (P<0.001) varied with the years. The results emphasize the need for greater management intervention to reduce the incidence of reproductive problems in sub tropical cattle herds.

Defining the primary business measure of liveweight production for beef cows in northern Australia

Context Annual liveweight production of a cow is the sum of the weight of its calf at weaning and its own annual liveweight change. Along with value per kg, annual liveweight production constitutes the business income contributed by the animal; however, it is not well described for north Australian beef herds. Aims This study aimed to quantify cow liveweight production and to measure impacts of reproduction and other risk factors. Methods Liveweight production data from 2122 Brahman and tropically adapted composite cows aged 2.5–8.5 years and grazing the four primary country types in northern Australia were analysed as a function of current and previous mating outcomes, mating age, breed, hip height, and body condition or liveweight. Key results Cow liveweight production was highly variable (coefficient of variation 40%) among and within years. Liveweight production of cows averaged 154 kg/year from their first mating, 168 kg/year from their second, and 190 kg/year from subsequent matings; however, production efficiency remained constant, with a liveweight production ratio of 0.31–0.32 kg produced annually per kg of grazing animal. Within environment, average weaner production (kg/cow) approximated the estimated average annual weight gain of yearling cattle. Weight of calves weaned contributed ~87% of annual liveweight production. Liveweight production averaged 103–143 kg higher for cows that weaned a calf than those that lost a calf, with the effect greater in older cows (P < 0.001). Liveweight production averaged 39–43 kg higher for non-pregnant cows than those that lost a calf (P < 0.001). These effects were attenuated by ~20% over a lifetime. Cows weaning a calf from a previous mating had liveweight production 57–85 kg higher (P < 0.001) than those not weaning a calf, having begun the year in poorer condition because of lactation. Calf weaning weight was 25 kg higher in mature cows than in first- and second-lactation cows. Liveweight production advantages of tropical composites over Brahmans appeared primarily associated with consistently higher calf weaning weights, and higher cow growth during their first reproductive year. Conclusions This research successfully demonstrated the concept of liveweight production in breeding beef cows, showing it to be primarily governed by available nutrition and mating outcome. Implications These findings provide a previously unavailable reference point for beef-systems management in northern Australia; for example, liveweight production could be used to determine the potential achievable increases in cow performance for a specific nutritional environment.

The use of Hereford sires over mature Angus dams can add value to Angus cattle herds

Context Overseas studies have quantified production differences of Hereford × Angus compared with purebred Angus for a range of traits including growth, carcass and reproductive traits. Aim This study aims to provide a comparison of Hereford × Angus and purebred Angus under modern grazing conditions in southern Australia. Methods Thirty Hereford and 22 Angus sires were mated to 1100 Angus cows and heifers in a large commercial herd run on pasture at Musselroe Bay, Tasmania. Approximately 1650 calves were born. Steers were grown on pasture for an average of 23 months and then slaughtered. Results Hereford sired calves were heavier at birth (+8.8%) and weaning (+4.1%). Hereford-sired calves from heifers (but not from mature cows) had more assisted births (+8.2%) and more calf deaths (10.0% vs 5.1%). Hereford-sired steers had higher hot standard carcass weight (+4.1%) and eye-muscle area (+3.2%) but when hot standard carcass weight was fitted as a covariate, eye-muscle area was no longer significant. Carcass quality measures (AUSMEAT marbling –25.8%, Meat Standards Australia marbling –10.5%, Meat Standards Australia index –1.0%) were poorer for Hereford-sired steers and fat colour (+6.9%) was darker. Meat samples from Hereford-sired steers had significantly lower colour indicators (L and b). There was no difference in cooking loss and shear force, and intramuscular fat was lower (3.0% vs 4.1%). Conclusions Hereford × Angus calves were heavier at birth than were purebred Angus, but had more calving difficulty and deaths associated with heifer dams. Hereford × Angus carcasses were heavier but had lower indicators of quality than did purebred Angus. Implications As Hereford × Angus steers produced a 4.1% heavier carcass, pure Angus steers would need to attract a premium of at least 4.1% for the additional marbling to give more value. Hereford bulls could be mated to Angus cows and not Angus heifers to avoid calving difficulties. Alternatively, good calving Hereford bulls could be selected using estimated breeding values when mating to Angus heifers.

PRODUCTIVITY OF COWS OF DIFFERENT GENOTYPES IN THE AUE “LYAKHOVICHSKOE-AGRO”

When analyzing the milk performance of cows for 305 days of complete lactation, it was found that animals of the first and second lactation were less productive (milk yield: 6916 and 7596, respectively) than mature cows of the third lactation and older (7904 kg of milk). The milk production coefficient varied in the context of lactations from 1208.6–1340.0 which characterizes them as dairy cattle. The daughters of bulls with the breeding value index of 100 and above had the highest milk yield – 7531.8 kg of milk, which is 50.6 kg more than the herd average.

Selection strategies for beef cow size and condition

Context The present work was motivated by beef breeder concerns that selection for high growth and low fat in steers and low mature weight in cows will lead to cows that have low body condition and, therefore, productivity. Aims The aim of this was to partition cow weight into size (associated with height) and condition (variation net of height) and test whether the trait net weight is a worthy addition to breeding programs. Methods Angus cows (5901) were measured as heifers (4889) and at pre-calving and weaning of their first and second calf (minimum 2690) for weight, height and body condition traits (condition score, ultrasound eye-muscle area, P8 and rib fat depth, and intramuscular fat percentage). A novel trait was developed by fitting height as a covariate to weight, with the residuals termed net weight. Key results Net weight was both heritable and genetically correlated with cow condition score and ultrasound measures. However, despite having a lower heritability, condition score was a more effective measure for genetic improvement of cow condition. Conclusions A measure of cow condition should be included in genetic evaluation programs but net weight is unlikely to be that measure. Implications Condition score should be recorded at the time of mature cow weight for breeding programs.