Vesna Gantner

Effect of α-linoleic acid supplementation in goat's diet on milk yield, quality and somatic cell count

Abstract Investigation of the effect of α-linoleic acid (ALA) on goat’s milk production (daily milk yield, fat and protein content) and somatic cell count (SSC) and the persistence of this effect after supplement termination was conducted on 32 Alpine breed goats kept on an indoor Alpine farm. After adaptation period the animals were randomly allocated according to treatment into control group (G0) with no added supplement and test group (G1) where supplement containing ALA was added over a period of five days. Measurements of milk yield and sampling for analysis of milk composition in adaptation period, treatment period and first five days of period after treatment occurred every day at each milking (morning and evening). From the 5th to the 50th day of the after treatment period, measurements and sampling occurred every fifth day. Based on the conducted research it could be concluded that supplementation had no effect on milk yield; it had low effect on milk components and significant effect on SSC. This could be used as a method of choice for reduction of SCC in goat’s milk.

Comparison of statistical models to estimate daily milk yield in single milking testing schemes

Abstract Different statistical models were compared to estimate daily milk yield from morning or evening milking test results. The experiment was conducted on 14 family farms with 325 recorded cows. The amount of explained variance was higher for models including the effects of partial milk yield, the interval between successive milking, the interaction between partial milk yield and the milking interval and the farm (R2 = 0.976 for AM, R2 = 0.956 for PM) than for models including partial milk yield effect only (R2 = 0.957 for AM, R2 = 0.937 for PM). Estimates of daily milk yield from linear models were more accurate than those obtained by doubling single milking weights. The results show that more complex model gives the best fit to the data. Differences between models according to determination and correlation coefficient were minor. Further investigations on larger sets of data are needed to draw more general conclusion.

Methods for estimation of daily and lactation milk yields from alternative milk recording scheme in Holstein and Simmental cattle breeds.

Abstract The aim of this study was to compare different statistical methods for the estimation of daily and 305-day lactation milk, fat and protein yields of Holstein and Simmental cattle breeds using an alternative milk recording scheme. Data included 6,824 individual test-day milk yield records collected according to the A4 milk recording method on 668 cows reared on 15 family farms. Daily milk, fat and protein yields were estimated using several statistical methods with regard to breed. The 305-day lactation yields were calculated from estimated daily yields using the Test Interval Method. The correlation between estimated and true yields, as well as the mean difference among estimated and true yield were used as the evaluation criteria for estimation methods. The linear regression of daily to partial milk, fat and protein yields while taking into account the interval between successive milkings was shown to be the most accurate model for estimating daily values, either from morning or evening records. The simple doubling of morning or evening records overestimated and underestimated the daily yields, respectively. When 305-day lactation milk, fat and protein yields were compared no difference between evaluated methods were found. Also, a separate estimation of daily and 305-day lactation yields according to breeds did not result in increased estimation accuracy.

Influence of temperature-humidity index (THI) on daily production of dairy cows in Mediterranean region in Croatia

With the aim of analysis the influence of temperature-humidity index (THI) on daily performance of dairy cows in Croatian Mediterranean region, 217,509 test-day records collected from January 2005 until April 2010 were extracted from HPA (Croatian Agricultural Agency) database. Milk recording in Croatia occurs according to the alternative milk recording method every four weeks, therefore, daily production of milk yields and components was projected using projection parameters estimated in authors’ earlier research (Gantner, 2008). Logical control of data was performed according to ICAR standards (2003). The yields recorded after the 500th lactation day was deleted from the dataset. According to the parity, cows were divided into three classes (heifers, cows in second lactation and cows in third and higher lactations) while, regarding the calving date, cows were divided in two calving season subgroups. According to the test date, four measuring season subgroups were created. Based on temperature and relative humidity recorded in stable at each milking control the daily temperature-humidity index (THI) values were calculated using the equation by Kibler (1964). For estimation of the influence of exceeded THI (above critical value -72) on daily production of dairy cows statistical model that take into account effects of lactation stage, breed, calving season, measuring season as well as effect of THI group (T1 - THI under critical value; T2 - THI above critical value). The significance of differences between the means of the daily milk, fat, protein and lactose yield, as well as between the means of the daily fat, protein, and lactose content within the THI classes in regard to parity classes was tested with Scheffe test. For the statistical analysis and the figures drawing the SAS/STAT package was used (SAS Institute Inc., 2000). The exceeded THI significantly decrease daily milk, fat, protein and lactose yield in heifers and cows in third and higher lactations. In second lactation determined decrease was not significant. Highly significant decrease of daily fat and protein content was determined in all cows, regardless the parity. The daily lactose content was not significantly influenced by enhanced value of THI. Management strategies are needed to minimize heat stress and to attain optimal cows’ production in climatic condition of Croatian Mediterranean region.

Differences in response to heat stress due to production level and breed of dairy cows

The climatic conditions in Croatia are deteriorating which significantly increases the frequency of heat stress. This creates a need for an adequate dairy farming strategy. The impact of heat stress can be reduced in many ways, but the best long-term solution includes the genetic evaluation and selection for heat stress resistance. In order to create the basis for genetic evaluation, this research determined the variation in daily milk yield (DMY) and somatic cell count (SCC) as well as the differences in resistance to heat stress due to production level (high, low) and breed (Holstein, Simmental) of dairy cattle breed in Croatia. For statistical analysis, 1,070,554 test-day records from 70,135 Holsteins reared on 5679 farms and 1,300,683 test-day records from 86,013 Simmentals reared on 8827 farms in Croatia provided by the Croatian Agricultural Agency were used. The results of this research indicate that the high-producing cows are much more susceptible to heat stress than low-producing especially Holsteins. Also, the results of this research indicate that Simmental breed, in terms of daily milk production and somatic cell count, could be more resistant to heat stress than Holstein. The following research should determine whether Simmentals are genetically more appropriate for the challenges that are in store for the future milk production in this region. Furthermore, could an adequate production level be achieved with Simmentals by maintaining the heat resistance?

Prevalence and aetiology of subclinical mastitis in goats

Abstract The study was conducted in 2006 on 20 French alpine goat farms in Croatia. Milk samples were taken from each udder half, for the mastitis test and the bacteriological test, 2120 samples in total. Subclinical mastitis was diagnosed in 211 out of 1060 goats, or in 20% of the studied population. Mastitis of one udder half was diagnosed in 84% of the affected population, while mastitis of both udder halves was diagnosed in 16% of the affected goats. A positive mastitis test reaction was identified in 605 samples (28%), and the pathogenic bacterium was isolated from 244 of these samples (36%). From 22 samples (1.5%) which were negative to mastitis test, pathogenic bacteria, namely S. aureus (21 samples) and Streptococcus D (1 sample), were isolated. Staphylococcus aureus was isolated from 72% mastitis test positive samples, coagulase-negative staphylococci in 16%, other bacteria were isolated from a smaller number of samples: Streptococcus D (6%), Bacillus spp. (2%), and E. coli (2%). The results of the study lead to the conclusion that the subclinical mastitis in goats has a prevalence of 20% on average which increases with higher lactation number. Staphylococcus aureus is the primary causative agent of the inflammations.

Prediction of lactation milk yield using various milk recording methods

The objective of this study was to determine the effect of various milk recording methods (A4, AT4, A6, AT6) on prediction accuracy of 100, 200 and 305-day milk yield. The data used in this study were 11,430 individual test-day milk yield records collected from November 2004 to November 2006 on 813 cows reared on 15 family farms in Croatia. Milk recording was performed according to A4 and A6 milk recording method by the field officer of the Croatian Livestock Centre. From the corrected database with test-day records, two different datasets were created. The first dataset (A4; n = 7,500) included test day records collected every four weeks, while the second dataset (A6; n = 3,830) included test day records collected every six weeks. When lactation milk yields were predicted from alternative milk recording methods (AT4, AT6), daily (24 h) milk yield was estimated from single evening or morning milk yield using linear model that taken into account effect of interval between successive milkings. Lactation milk yield was calculated for three different days in milk (100, 200 and 305 days) using the Test Interval Method (TIM) that is reference method by ICAR (ICAR, 2003). Results show that the alternate milk recording method at 4-week intervals provides low bias and high accuracy of prediction of 100, 200 and 305-milk yields, while milk recording methods at 6-week intervals gives prediction of 305-milk yield with higher bias and lower accuracy.

Test-day records as a tool for subclinical ketosis detection.

The prevalence, as well as the effect of subclinical ketosis on daily milk yield, was observed using 1.299, 630 test-day records collected from January 2000 to December 2005 on 73, 255 Slovenian Holstein cows. Subclinical ketosis was indicated by the fat to protein ratio (F/P ratio) higher than 1.5 in cows that yielded between 33 to 50 kg of milk per day (Eicher, 2004). The ketosis index was defined in relation to the timing of subclinical ketosis detection to the subsequent measures of test-day milk yields. The effect of subclinical ketosis on test day milk yields were studied separately for each parity using the mixed model analysis. The statistical model included the fixed effect of ketosis index, calving year-month, lactation stage and random effect of animals included in the study. The prevalence peak of subclinical ketosis occurred in the first month of lactation. Subclinical ketosis had a significant negative effect on daily milk yield. Decrease in milk yield in the amount of 4.21 kg/day, 2.73 kg/day ; 2.78 kg/day ; 2.83 kg/day ; and 3.72 kg/day in each parity were determined within 35 days after the detection of subclinical ketosis. The decrease continued in subsequent milk controls. The research results show that test-day records could be a useful tool for early detection of subclinical ketosis.

11. Effect of Heat Stress on Metabolic Disorders Prevalence Risk and Milk Production in Holstein Cows in Croatia

Abstract The objectives were to evaluate the effect of heat stress on daily milk traits (yield, fat and protein content, F/P ratio) as well as to determine the differences in metabolic disorders (acidosis, ketosis) prevalence risk regarding the heat stress conditions. For statistical analysis 1,187,781 test-day records of milk, fat, and protein from 89,030 Holsteins reared on 6,388 farms provided by the Croatian Agricultural Agency, were used. Based on the results it could be concluded that heat stress condition causes decline of daily milk yield and components as well as increase of acidosis risk regardless of the lactation stage and increase of ketosis risk during mid-lactation. The research results point out that the test-day records and environmental measurements collected in regular milk recording could be used as a tool for dairy herd monitoring enabling the early detection of unfavourable environmental conditions and the subclinical disorders. Since environmental conditions significantly affect daily milk yield and components, and consequently F/P ratio, further research with the purpose of detailed formulation of metabolic disease risk in relation to the environmental conditions is needed.

Analysis of inbreeding in Slovenian Haflinger population

Abstract The pedigree information of 3613 animals registered in the Slovenian Haflinger stud book from birth year 1905 to 2008 were analysed using PROC INBREED in SAS/ STAT with the purpose of analysis of inbreeding level in Slovenian Haflinger population. Relationship (R) analysis was restricted to possible mating partners that had offspring born between 2004 and 2008 (i.e., 323 mares and 58 stallions). An increasing trend of inbreeding coefficients (F) was observed in recent years, although a generally low F was detected. Mean values of R between possible mating partners were mostly around zero, while maximum values ranged up to 0.63. The development of application that would ease the calculations of F and R could help breeders to prevent related mating in the future.