Growth Rate Of Heifers Research Articles

How increased heifer growth rate and reduced dairy cow replacement rate can improve farm economy and reduce greenhouse gas emissions - a win to win situation?

Rearing of replacement heifers makes up a significant part of the total costs in dairy farming. Nevertheless, the average age at first calving for dairy heifers still stays well above 2 years in many countries. This study examined the economic and environmental impacts of increased heifer growth rates and reduced replacement rates on Norwegian dairy farms. The current average growth rate in Norway (baseline scenario) was compared to an accelerated growth rate scenario. Within each of the two growth rate scenarios, we compared three different cow replacement rates. A farm account survey dataset containing physical and economic data on 311 Norwegian farms was clustered into three farm groups: small, medium, and large. To model economic consequences, we used the whole-farm linear programming model ScotFarm. A life cycle analysis model was used to model the environmental impacts of the baseline scenario and an accelerated growth rate scenario on the three farm groups. Accelerated heifer growth rate had a positive effect (14–28%) on farm annual gross margin depending on farm size. While accelerated growth rate resulted in only minor reductions in total emissions at farm level compared to the baseline scenario, reduced replacement rate lowered total farm level emissions by up to 8%, and emissions per unit of output by up to 6%. We conclude that an accelerated heifer growth rate scenario could potentially increase farm gross margin by some 14–28% compared with a baseline growth rate scenario. Reducing the replacement rate would be more efficient to reduce farm−level greenhouse gas emissions.

ВЛИЯНИЕ ЖИВОЙ МАССЫ МОЛОДНЯКА НА ПОСЛЕДУЮЩУЮ МОЛОЧНУЮ ПРОДУКТИВНОСТЬ ПЕРВОТЕЛОК В РАЗНЫХ КЛИМАТИЧЕСКИХ ПОЯСАХ РОССИЙСКОЙ ФЕДЕРАЦИИ

The purpose of research is to study the effect of live weight of heifers at the age of 6 months on their subsequent milk production. Objectives: to study the growth rate of heifers with different live weights at 6 months; to assess the level of milk productivity (milk yield, mass fraction of fat and protein, amount of milk fat and protein) in first-calf heifers with different live weights at 6 months. The study included more than 25 thousand first-time Holstein heifers of the same genotypes (lines), bred in four climatic zones co-vering the territory of the Russian Federation. These zones include subtropical, temperate continental, extreme continental and arctic climates. The regions of the Far North with the most severe and cold climate, unsuitable for breeding Holstein dairy cattle, were not taken into account. Data from the Selex information system were used for the analysis. Statistical processing of the obtained data was carried out on the basis of generally accepted methods of variation statistics (using MS Excel). The reliability of the difference bet¬ween the compared values was determined using the significance criterion according to the Student's table. It was found that the live weight of calves at 6 months has a certain influence on the subsequent milk productivity of first-calf heifers. However, the optimal live weight varies depending on the climatic zone. Thus, in a subtropical climate, the optimal live weight is more than 175 kg; in a temperate continental climate – more than 185; in a sharp continental climate – less than 166; in a harsh arctic climate – over 200 kg. These results make it possible to optimize the breeding process and ensure maximum milk production in different climatic conditions.

Adaptation of the Third Generation Aberdeen Angus Heifers in the North Kazakhstan Region

The article presents research materials on the adaptive and productive qualities of the third-generation heifers of Aberdeen Angus cattle in the conditions of the "Zholdasbay-agro" farming enterprise of the North Kazakhstan region. The object of study was the growth and development of third-generation heifers obtained by Canadian and European selection of the Aberdeen-Angus breed. According to the results of the study and the summary of clinical signs, the frequency of antenatal hypotrophy in newborn calves of the Aberdeen-Angus breed of Canadian selection was 12.3%, European 8.7%. The research results showed that the relative growth rate in European calves up to 6 months is higher than in peers of Canadian breeding, but in the period from 6 to 8 months, calves obtained from cows of the second generation of Canadian breeding are superior to calves of European selection. The established tendency of a lower growth rate of heifers obtained from cows of Canadian breeding may be associated with an increase in the tension of regulatory mechanisms that ensure the adaptation of animals to new environmental conditions.

Features of growth and development of young cattle of Hereford breed of different origin

Relevance. In recent years, there has been a decrease in the total number of cattle of both meat and dairy production. In this regard, the study of the features of breeding of beef cattle is relevant. In the studies, the growth and development indicators of the young cattle of Hereford breed were studied, depending on their origin.Methods. The research was carried out in the conditions of a breeding reproducer of LLC "Chebomilk", Cheboksary district of the Chuvash Republic. The dynamics of growth and development were studied by monthly weighing of animals. In newborn calves at the age of 205 days, 6, 8, 9 and 12 months, and in heifers additionally at 15 and 18 months, the height in the sacrum was measured. Based on the data from the weighing results, the absolute and average daily increase was calculated.Results. It was found that the growth rate of heifers and calves on fattening is influenced by the genotype of the father. When comparing the average live weight of young animals at the age of 18 months, the best results were in bulls received from the bull Perets — 375.8 ± 17.5 kg, this is 3.8 kg more than the same indicator for bulls received from the bull Timeline and 7.8 kg more than the bull Emuleishn, and by the live weight of heifers at the age of 18 months the Timeline is leading — 352.6 ± 25.2 kg. Bulls and heifers — descendants of the bull Perets of the Mayer-Verne 88480 line are distinguished by the best growth rate. The average daily increase at 18 months of age in bulls was 931 ± 57.2 g, in heifers — 577 ± 54.1 g, which is higher than their peers by 1.2–12.2%. To improve the productive and breeding qualities of the Hereford breed, it is recommended to carry out targeted selection and selection of parental pairs.

Dairy productivity of Yenisei red-motley cows as a function of growth rate and age of fertile insemination

The main task in dairy farming is the proper breeding of heifers to realise their genetic potential further. The research aims to study the impact of the growth rate of heifers and heifers of Yenisei type of red-motley breed on their subsequent dairy productivity. The research was conducted in the breeding plant of Solgon JSC of the Uzhur district, Krasnoyarsk Territory. The heifer population (1156 heifers) was divided into eight groups according to the age of fertile insemination. The first three groups were fast-growing animals (10-14 months of fertile insemination), the remaining five groups were slow-growing animals (15 months of fertile insemination or older). The authors chose the following indicators to study: live weight, average daily live weight gain, age of first successful insemination and first calving, and milk productivity of cows in 305 days of the first lactation. Fast-growing heifers were found to outperform slow-growing heifers in terms of growth rate. The live weight of fast-growing heifers was 102 grams greater, or 11.6% than that of slow-growing heifers from birth to first fertile insemination. The live weight of fast-growing heifers was 83 grams or 11.3%, more outstanding from birth to first calving. A comparative analysis of the milk production of fast- and slow-growing animals showed no significant difference between the groups on average. However, the difference in milk yield and milk fat and protein between the individual groups was statistically significant. Studies have confirmed that heifers of the Yenisei type can be inseminated quite successfully at an earlier age (12-14 months). Heifers of this type enter the production group more quickly and cost less to raise (by 4,742 roubles or 11.9%), which has an impact on profit (by 5,844 roubles or 30.2%) and profitability levels (by four percentage points or 40%).

THE GROWTH AND REPRODUCTIVE ABILITY OF HEIFERS AND FIRST-CALF COWS UKRAINIAN RED AND BLACK-SPOTTED DAIRY BREEDS IN THE CONDITIONS OF THE CENTRAL REGION OF UKRAINE

THE GROWTH AND REPRODUCTIVE ABILITY OF HEIFERS AND FIRST-CALF COWS UKRAINIAN RED AND BLACK-SPOTTED DAIRY BREEDS IN THE CONDITIONS OF THE CENTRAL REGION OF UKRAINE

INFLUENCE OF PARATYPIC PARAMETERS ON THE EFFICIENCY OF BREEDING OF HEIFERS

The article examines the effectiveness of heifers under the influence of paratypic parameters. Parameters of efficiency of heifers at the “Gontarivka” breeding facility were 1.2153 times worse than the indicators at “Profintern” breeding facility in 2018; for 2019 - 1.3449 times and for 2020 - 1.2372 times. Multicriteria analysis takes into account such parameters as the age of the first insemination and the number of heads in the insemination groups. It was found a special advantage of soybean meal usage according to the considered criteria when it was 0.0119 and for sunflower meal – 2.3697 times less. The probable influence of the year on the growing intensity of young stock (p<0.001) was established. Thus, the strength of the influence of this parameter in the breeding facility “Gontarivka” was 0.8%, in “Kutuzivka” breeding facility it was 4.1% and in “Stepne” breeding facility it was 1.8%. The growth rate of heifers during the study period in all farms changed slightly. The increase in the average daily weight gain between 2018 and 2021 in the “Gontarivka” breeding facility was 124 g, in the “Kutuzivka” - 164 g and in the “Stepne” - 27 g (p <0.001). The same patterns in changes in average daily increments over the years in all farms indicate their dependence on climatic conditions of the season. The dynamics of changes in the growth of heifers depending on their age was also determined, the strength of which was 5.26% in “Gontarivka”, 7.43% in “Kutuzivka” and 7.43% in “Stepne” (p <0.001). The average daily weight gain also depended on the average monthly air temperature. The strength of the impact of this factor was 17.7% in “Gontarivka”, 13.6% in “Kutuzivka” and 9.6% in “Stepne” (p <0.001). Analysis of the dynamics of changes in average daily weight gain for the whole period showed that in the summer with increasing air temperature decreased. Conversely, in winter, when keeping heifers indoors, the average daily gain increased. The correlation coefficient between the growth of heifers and the average monthly temperature in "Gontarivka" was negative (r = -0.159, p <0.001), and with the age of animals - positive (r = +0.039, p <0.01). For “Kutuzivka”, the values of the coefficients in the direction of communication did not differ and amounted to -0.159 (p <0.001) and +0.190 (p <0.001), respectively. According to the data of animal development of the State Enterprise "Stepne" positive correlations of growth with the age of heifers (r = +0.187, p <0.001) and with the average monthly air temperature (r = +0.151, p <0.01). Based on the results of calculations, models for forecasting average daily increments for experimental farms have been developed.

The growth rate of heifers of the Ukrainian black and white spotted dairy breed as a precondition of high productivity

The growth rate of heifers of the Ukrainian black and white spotted dairy breed as a precondition of high productivity

THE RELATIONSHIP BETWEEN GROWTH RATES OF KYIV FACTORY TYPE UKRAINIAN BLACK-AND-WHITE DAIRY BREED HEIFERS AND COWS LIFELONG PRODUCTIVITY

The studied of Kyiv factory type Ukrainian Black-and-White dairy cows productivity depending on heifers average daily gain. The studied of 1071 animals lifelong use data. Cattle was divide into 5 groups according to the values of average daily gains at the age of 0-3; 3-6; 6-12 and 12-15 months. Animals distributed on the standard deviation from average daily gain of the herd. In animals included in the groups studied the productivity of the first lactation and the period of productive use. It found that increase the heifer’s growth rate leads to decrease in the age of the first calving. The age of the first calving is most affect by the growth rate up to 3 months of age. Preservation of the first calving cows increases when the growth rate of heifers is slightly higher than the average herd. The highest survival of the first calving cows (93.8 %) obtained providing growing heifers aged 3-6 months with increments of 658-853 g. The highest milk yields during the first and highest lactation were obtain by growing heifers aged 6-12 months with an average daily gain over 710 g. Animals with the highest growth rate at other ages had a lactation graph with several peaks, which indicates their increased sensitivity to changes in conditions of use. The bath-shaped udder founded are more common in slow-growing animals from birth to 12 months. The increase in average daily gain led to an increase in the proportion of cows with rounded and cup-shaped udders. The not installed relationship between the average daily gain of heifers and the duration of the open data period and the period between calving. These traits are more relate to the milk production of cows than to the growth of heifers. The greatest duration of lifetime use, milk yield and number of calves during life were at the growth rate of heifers from birth to 12 months at the level of + 0.5σ… + 1.5σ to the average for the herd. A further increase in the growth rate during these periods led to a decrease in the duration of productive use by 0.4… 1.1 years and a lack of 0.4… 0.9 calving. Animals that at the age of 12-15 months had a growth rate at the level of the average herd with deviations within ± 0.5σ were marked by a long productive period. Studies prove the possibility of increasing the lifelong productivity of livestock by heifer’s selection at a growth rate from birth to 15 months.

Effect of whole-milk allowance on liveweight gain and growth of parenchyma and fat pads in the mammary glands of dairy heifers at weaning

The rates of development of 2 tissues in mammary glands, parenchyma (PAR) and the mammary fat pad (MFP), in response to nutrition in early life might have a major bearing on lifetime milk production. Historical studies reported that feeding greater amounts of dietary nutrients from postweaning to puberty increased growth rates of heifers and stimulated the growth of MFP at the expense of PAR, which might suggest compromised mammary development and future milk production. The current study sought to determine if a higher volume of whole milk (8 vs. 4 L/d) offered to calves would increase rates of growth and development of PAR in mammary glands at weaning (1 to 12 wk). To measure these tissues, we developed 2 simple methods to assess the size of PAR and MFP at the time of screening using ultrasound. We report that calves offered 8 L/d of whole milk had greater rates of growth until weaning (0.86 ± 0.06 vs. 0.81 ± 0.09 kg/d), compared with calves offered 4 L/d. Ultrasonography showed that despite the faster rates of growth in calves offered 8 L/d of milk/d, the ratio of PAR:MFP depth was 40% less at weaning in the front glands (34%) compared with calves offered 4 L of milk/d. Rear glands were less impaired. The ultrasound methods developed here might be useful to monitor the development of mammary glands in response to different nutritional regimens during the preweaning period.

Long term beef production in extensive cow-calf systems in the tropical savannas of eastern Colombia

Replacement beef heifers in extensive systems of the neotropical savannas of Colombia are low priority animals and are assigned to native savannas and low-quality pastures, with scarcely researched long-term consequences. The study pooled data from four contemporary grazing experiments to determine the effects of low growth rates of heifers on their lifetime production of liveweight gains (LWGs) per year and per hectare (ha) subject to different management strategies. Three growth rates were imposed on grazing heifers during the growing phase (i.e. nine-36 months of age) on Brachiaria humidicola pastures. Upon the end of the previous phase, animals were allocated to a B. humidicola paddock with a reduced stocking rate or introduced to a B. decumbens sward to allow compensatory LWGs during the breeding phase (i.e. cows plus weaned calves). Severely limited heifers allowed to make compensatory growth did not reach the outputs of better fed animals. Regardless of the strategy followed, high producing years tended to be followed by lower production in the following year. Comparison with reasonably fed breeding cows full-time on well-managed B. decumbens showed important and significant differences in favor of the more intensive system over the lifetime of the animals. Over the nine-year period, the systems’ beef output (i.e. weaned calves plus cows’ LWGs) ranged between 86 and 206 kg/ha/year and demonstrated that a wide array of low input management alternatives is feasible. Beef output increases if the LW of cull cows is considered, particularly if they are allowed a short period of fattening during the rainy reason on a low input pasture.

Impact of FMD outbreak on milk production and heifers’ growth on a dairy herd in southern Iran

Foot and mouth disease is endemic in Middle Eastern countries including Iran but its impact is poorly characterized. The present study was conducted to evaluate the impact of FMD outbreak on milk production and heifers’ growth in an industrial dairy herd located in Fars province, southern Iran. Data about individual milk production, heifers’ growth and total daily milk (sold for manufacturing), its fat and protein content and somatic cell counts were collected from the herd database. Based on the results of the linear mixed models, a significant decline in individual milk production after the outbreak was observed compared with before the outbreak. There was a total reduction of 8.0 and 4.7% in mean daily milk production per cow after the outbreak when compared with before (over a 42days outbreak period) in lactation one (P<0.001) and lactation ≥2 cows (P=0.024), respectively. The total daily milk (P=0.027) and protein (P=0.002) showed significant decline during the outbreak period. The fat content decreased after the outbreak (P=0.014). Somatic cell counts did not show significant changes. The recorded heifers’ weights (4–17 months of age) showed 7.1kg decrease after the outbreak in comparison with the period before that (P<0.001). In conclusion, we observed a negative impact of FMD outbreak on milk production and heifers’ growth in study herd. The impact on daily milk production was less than the values reported previously. This difference could be attributed at least partly to differences in livestock genetics and management practices. Lower growth rate of heifers after the outbreak period could potentially extend the age at first calving. It is suggested that farmers are educated on awareness and preparation for infectious disease outbreaks and to practice good management routines that could potentially reduce the economic impact of these diseases.

Efficacy of methane-reducing supplements in beef cattle rations

The objective of the present study was to evaluate the effect of including a pellet containing feed components targeted at methane-producing microbes and methane-producing biochemical pathways, into the ration of beef cattle in southern Australia. The so-called ‘methane-reducing supplement’ (MRS) components were chosen from readily available and inexpensive sources to ensure high adoption of the practice if successful. The effect of the pellet on animal performance, diet DM digestibility and gas emissions (measured using an open-circuit gas quantification system) of beef cattle in comparison with animals fed a control diet or high-quality supplement (HQS) was evaluated. In the first trial, there were no differences in DM and digestible energy (DE) intake, but the methane emission in g/day, g/MJ of DE intake (P &lt; 0.01), and in g/kg of DM intake (P = 0.01) were lower for steers fed MRS. There was also a trend to lower carbon dioxide emission (g/MJ of DE intake) in steers fed MRS (P = 0.07). In the second trial, heifers fed the MRS produced 18.7% less carbon dioxide (P &lt; 0.01) and 15.5% less methane (P = 0.01) than heifers on the HQS supplement, when expressed in g per unit supplement intake on a bodyweight basis. There was no difference in growth rate of heifers on the HQS and MRS supplements. Combining methane-inhibiting feedstuffs derived from agro-industrial by-products into supplements for cattle in southern Australia appears to be an effective means of reducing methane output and methane intensity from grazing beef cattle.

Measuring the growth rate of UK dairy heifers to improve future productivity

Sub-optimal heifer growth is associated with higher disease rates and reduced future performance and longevity in the dairy herd. This report describes a system for measuring heifer growth from birth to first calving that was used on commercial dairy farms in South West England, in order to gather benchmarking data to feed back to farmers. Weights (n = 8443) were collected from 20 farms.There was a marked variation in individual and herd mean growth rates. Overall, calves gained no weight in the first 8 days after birth and had a very low growth rate (median 0.12 kg/day) up to 30 days, a period when feed conversion efficiency is high and calves are vulnerable to disease. Heifers whose growth rate up to 180 days was low were significantly less likely to achieve target service weight (374 kg) by 420 days. Monitoring heifer growth during the rearing period enables farmers to improve heifer growth rates and so impact both the efficiency of heifer rearing and, potentially, the productivity and performance of the adult herd.

Performance of Zebu Heifers under Heat Mitigation Measures in a Humid-Tropical Environment

Abstract Productivity of bovine species is drastically reduced when the animals are subjected to heat stress as often occurs in tropical regions. Although zebu cattle are considered to be heat tolerant, their productivity could improve when cooling measures are applied to mitigate the effects of heat stress. In this study, twenty four Sokoto Gudali heifers under mean ambient temperature of 27.4 ­°C and temperature humidity index (THI) of 78 were subjected to four cooling treatments: no cooling (control), fan, shower and shower with fan. Rectal temperature of heifers reduced from 39.3 °C (in the afternoon) to 39.2, 38.5, 38.5 and 38.0 °C for control, fan, shower and shower with fan, respectively, one hour after administration of treatments. Dry matter intake (DMI) and growth rate of heifers increased significantly (P &lt; 0.05) when cooling measures were applied. DMI of heifers varied from 2.08 to 3.78% of body weight (BW) while average daily gain (ADG) varied from 0.38 to 0.86 kg/d with cooled animals having the higher values. Application of cooling measures significantly improved the performance of zebu heifers raised in a hot and humid environment.

Effect of dietary protein on intake, nutrients utilization, nitrogen balance, blood metabolites, growth and puberty in growing Bhadawari buffalo (Bubalus bubalis) heifers.

Fifteen Bhadawari buffalo heifers of 207 ± 9.78 kg mean body weight were randomly distributed into three dietary groups to evaluate the effect of protein level on nutrient utilization, nitrogen (N) balance, growth rate, blood metabolites, and puberty. All animals were offered wheat straw-berseem diets supplemented with concentrate mixtures of similar energy (2.7 Mcal/kg) and different protein levels (14.3-22%). Animals of standard-protein group (SPG) were offered protein and energy as per requirement, while animals of low-protein group (LPG) and high-protein group (HPG) were fed 20% less and 20% more protein, respectively, than SPG. Feed dry matter (DM) and metabolizable energy (ME) intake (% body wt. and g/kg w(0.75)) were similar for all three diets; however, the crude protein (CP) and digestible crude protein (DCP) intake on percent body weight and per kilogram metabolic weight was higher (P < 0.05) in HPG than in SPG or LPG. Digestibility of CP, cellulose, and hemicellulose was higher (P < 0.05) in HPG versus LPG. Fecal N excretion was similar, while urinary N excretion was highest (P < 0.05) in HPG (74.83 g/day) compared with SPG (50.03 g/day) and LPG (47.88 g/day), which resulted in lower N retention in HPG than in the other dietary groups. Level of dietary N had no effect on blood metabolites viz. glucose, urea, and N. Digestible energy (DE) and ME contents of diets were identical, while DCP contents were higher (P < 0.05) in HPG than in LPG. Feed and nutrient (CP and ME) conversion efficiency to produce a unit kilogram weight gain was identical among the dietary groups. Dietary protein level had no effect on the heifer's weight and age at puberty. The mean growth rate of heifers at 240 days was higher (P > 0.05) in SPG (330.8 g/day) than in LPG (296.7 g/day), while the animals gained more weight in January to March months and the lowest weight in May to July months. Protein level had no effect on conception rate of heifers. Results revealed that 20% higher or less protein than the ICAR requirement had no significant (P > 0.05) on feed intake, nutrient conversion efficiency for weight gain, heifer growth, and puberty; however, 20% more protein increased urinary N loss.

The impact of cow nutrient status during the second and third trimesters on age at puberty, antral follicle count, and fertility of daughters

Fluctuating feed resources to beef cows across the production cycle is a proven method for decreasing input costs; however, limiting nutrients during late gestation have been demonstrated to decrease ovarian follicle numbers in female offspring in some studies. We hypothesize that limiting nutrients to mature (≥3yr) crossbred beef cows during the second and third trimesters would result in daughters that would have decreased follicle numbers detectable by ultrasonography as yearlings. Over four breeding seasons, pregnant beef cows (n=397) were assigned to either Low (L), Moderate (M) or High (H) nutrient intake during the second or third trimester, resulting in four dietary treatment groups (L–H, L–L, M–H, and M–M). Heifers (n=416) born to these cows were weighed at weaning and moved to a dry lot where they were monitored for behavioral estrus with the aid of heat detection patches. Two weeks before their first breeding season, heifers were submitted for ultrasonographic examination of their ovaries to determine antral follicle numbers. Heifers were placed with bulls for 60d and pregnancy status was determined 45d after the bulls were removed. Growth and reproductive traits were analyzed using the MIXED Procedure of SAS with maternal diet and year as fixed effects. Maternal dietary intake did not affect heifer growth rates, age at puberty, or antral follicle counts (P≥0.40). However, an increased proportion of the heifers born to dams fed a high nutrient diet during the third trimester (L–H or M–H) calved in the first 21d of their first calving season (P=0.004). Antral follicle counts detectable by ultrasonography at yearling pre-breeding examination were greater in heifers that calved during the first 21d of their first calving season (P=0.02); however, these heifers did not differ in age at puberty (P=0.60). From this study, we conclude that: (1) limiting nutrient intake during late gestation in mature (≥3yr) beef cows does not influence the ovarian reserve or reproductive performance of daughters; (2) increasing maternal nutrient intake during the third trimester can improve the first service conception rates of daughters; and (3) pre-breeding ultrasonography to determine antral follicle counts is a good indicator of fertility for choosing replacement heifers.

COMPARISON ON ACCURACY OF LOGISTIC, GOMPERTZ AND VON BERTALANFFY MODELS IN PREDICTING GROWTH OF NEW BORN CALF UNTIL FIRST MATING OF HOLSTEIN FRIESIAN HEIFERS

The body weight records of 1221 heifers were used in this study collected from PT Taurus DairyFarm Sukabumi from year 2001 until 2011. The records that could be used for analysis were 373 out of1221 heifers, having completed data from birth to first mating period. Three different models i.e,Logistic, Gompertz, and von Bertalanffy were performed to analyze the growth rate of heifers. Theresults showed that the three models had different accuracy and heavily depend on age, environment andduration of recording. The body weights of sexual maturity and on certain ages were affected by theduration of recording. The Gompertz model was performed as the simpliest model in form ofcalculation. On the other hand, the Logistic was more difficult to calculate. All models indicated highaccuracy with the determination coefficient (R2) more than 90%. Based on the comparison, theGompertz and Logistic model are recommended for predicting the growth rate of heifers from birth tosexual maturity.

Effect of the provision of a low-nutritive feedstuff on the behavior of dairy heifers limit fed a high-concentrate ration

The objective of this study was to examine the behavioral and growth responses of dairy heifers when a low-nutritive feedstuff was provided with (either within or alongside) a limit-fed ration. Twenty-four Holstein dairy heifers (187±11.3 d of age, 231.1±12.0kg), divided in groups of 4, were exposed to each of 3 treatments in a replicated Latin square design with 28-d periods. The treatment rations were (1) total mixed ration (TMR) in a limited amount (TMR-L), (2) TMR in a limited amount with straw (1.8kg of DM/d per heifer) offered as a choice (TMR-SC), and (3) TMR in a limited amount with straw (1.8kg of DM/d per heifer) mixed in (TMR-SM). The TMR was fed, once daily, at a restricted level (2.02% of body weight) and contained (on a DM basis) 19.0% alfalfa/grass haylage, 21% corn silage, 45% high moisture corn, and 15% protein supplement. Feeding behavior and unrewarded time at the feed bunk were recorded for the last 14 d of each period. Standing time was recorded for the last 7 d of each period. Rumination behavior was recorded twice weekly (during the fifth hour after feed delivery) in the last 14 d of each period. Body weight was recorded weekly and group DMI was recorded daily. Dry matter intake was lowest for the TMR treatment compared with the treatments with straw (5.7 vs. 7.3kg/d). Heifer average daily gain tended to be lower on the TMR-SM treatment compared with the TMR-L and TMR-SC treatments (0.78 vs. 0.94kg/d). Feed efficiency (DMI/ADG) was improved on the TMR-L (6.3) compared with TMR-SC (7.8) and TMR-SM (9.9) treatments. Daily feeding time differed between the TMR-L (76.1min/d), TMR-SC (206.9min/d), and TMR-SM (279.2min/d) treatments. Unrewarded feeding time at the feed bunk differed between the TMR-L (38min/d) compared with the TMR-SC (10.9min/d) and TMR-SM (1.7min/d) treatments. Inactive standing time differed among treatments, with TMR-L being the highest compared with TMR-SC and TMR-SM (556.4 vs. 409.9 vs. 340.1min/d). There tended to be fewer heifers ruminating on the TMR-L compared with TMR-SM (14.0 vs. 21.9%). The results suggest that provision of straw as a choice alongside a limit-fed ration will allow heifer growth rates to be met, as well as provide a suitable foraging source that heifers can use to satisfy their natural feeding behavior patterns.

Factors influencing heifer survival and fertility on commercial dairy farms

The average dairy cow survives only three lactations, reducing the availability of replacement heifers. Prenatal losses occur due to early embryonic mortality (about 40%), later embryo loss (up to 20% in high-yielding herds) or abortion (about 5%). A recent survey of 19 UK herds showed that 7.9% of calves were born dead and 3.4% died within 1 month. During the rearing phase, 6.7% of animals were lost before reaching first service at 15 months due to disease or accident and another 2.3% failed to conceive. Many potential replacements therefore never enter the milking herd. This severely limits opportunities for on-farm selection of breeding cows in addition to presenting a welfare issue and causing economic loss. The most profitable animals once lactation is reached combine good milk production with a regular calving pattern. Some aspects of performance are related to age at first calving (AFC), which in turn is influenced by heifer growth rates. Poorly growing animals required more services to conceive, calved later and subsequently performed badly. Optimum fertility and maximum yield in the first lactation were associated with an AFC of 24 to 25 months. However, heifers calving at 22 to 23 months performed best in terms of total milk yield and survival over the first 5 years, partly because good heifer fertility was associated with better fertility later. We have investigated some possible juvenile predictors of future performance. Low-birth-weight calves were more likely to come from either primiparous mothers or older dams (3+ lactations) with higher peak milk yields, suggesting that the uterine environment may limit prenatal calf growth due to competition for nutrients with maternal growth or milk production. Linear trait classification scores for frame size show genetic correlations with longevity. The skeletal measures of height and crown rump length in 1-month-old calves was correlated to subsequent stature, and frame size was correlated to weight at 15 months. It may thus be possible to predict performance from simple size measurements as juveniles. Neither endogenous nor stimulated growth hormone (GH) release in 6-month-old calves were related to milk yield in the first three lactations, but size of a stimulated GH peak was positively related to milk energy values in the first lactation. Cows with delayed ovulation (>45 days) in the first lactation had a higher GH pulse amplitude and lower IGF-I as a juvenile. Cows that partition excess energy into milk in their first lactation may suffer reduced longevity.