Selection for Genetic heat tolerance: is it possible Summary box · 2016. 8. 22. · Selection for heat tolerance has been proven possible but up to date no official EBVs have been

Selection for heat tolerance has been proven possible but up to date no official EBVs have been published. Data required for such an evaluation are, in addition to pedigree and production and reproduction data, temperature and humidity from nearby weather stations. A study developing a national evaluation for heat tolerance in the US in 2005 has shown that the top 100 bulls for heat tolerance were lower in milk production, angularity and in somatic cell counts and higher for productive life, daughter fertility and TPI compared to the lowest 100 bulls. Selecting bulls for functional traits or for composite indexes that give enough emphasis to longevity, fertility and somatic cells are expected to indirectly favour heat tolerant genetic lines.

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by Fabiola Canavesi

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Summary box

n 1 | april 2016

GeneticSelection for heat tolerance: is it possible and how?Increasing temperature worldwide would create more frequently condition of heat stress for dairy cows. Temperature Humidity Index (THI) is the most common tool to quantify heat stress. At THI level above 72 dairy cows are outside their thermo-neutral zone and begin to adopt strategies to dissipate heat and minimize heat produced at metabolic level. These strategies affect their general health status and both productive and reproductive performances. In addition to structural solutions like

fans and water spray and changes in nutrition to support metabolic responses selection of animals that are naturally more tolerant to heat can be an additional tool that could help dairy farmers face stressful condition due to rising temperatures. Individual variations recorded under heat stress have been shown to have a significant genetic component.A national evaluation for heat tol-erance would require to combine production and reproduction data with information on temperature and humidity from wheather stations. Results from studies on Holstein herds in Georgia and Florida have shown that combining these data in a genetic evaluation model for production traits including a regression on THI at milk recording or at insemination

1. Average PTAs of top 100 bulls for heat tolerance and bottom 100 bulls for heat tolerance (Bohmanova et al., 2005. Interbull Bulletin. 33:160- 162.)

www.bioscreentechnologies.com

Focus on heat stress

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day allows to estimate the different response at genetic level in terms of production and reprodution traits. Genetic variance for heat tolerance has been found different from 0 only at a THI above 72 for production traits and 70 for NRR at 90 days.Estimated genetic correlation was around -0,30 between heat tolerance and production traits and around -0,41 between heat tolerance and reproduction traits like non return rate at 90 days (NRR90). Selection focused on production traits or fertility traits only will indirectly select cows that will result more sensitive to heat stress.A study developing a national

evaluation for heat tolerance in the US in 2005 used test day production record combined with wheather station data on temperature and humidity at milk recording in repeatability test day model with a random regression on THI level. Estimated sire Predicted trasmitting ability varied from -0.48 to +0.38 kg of milk per THI unit. The top 100 bulls for heat tolerance were: a) lower in milk production, dairy form and somatic cell counts; b) higher for longevity, fertility and TPI compared to the bottom 100 bulls. These differences suggest that sire selection focused on functional traits will indirectly select

cows that will be more tolerant to heat stress on milk production. The moderate size of genetic correlation between heat stress and both prodution and reproduction traits shows that genetic improvement for both production, reproduction and heat tolerance is possible if PTA for heat tolerance would be made available. Ongoing studies are using genomic information to identify genes involved in heat stress response and could be applied in genomic selection to recognize animals that show superior levels of heat tolerance together with PTA estimated in traditional quantitative models.

Health & Nutrition

by Alessandro Fantini

[email protected]

Guidelines for summer nutritionof dairy cows

Some guidelines for the nutrition of dairy cows in the summer. It is advisable not to further increase the intake of fat, of course only in rumen-protected form, to oppose to the energy intake reduction due to ingestion decrease.The sources of unsaturated fats that can easily go rancid, as those contained in the integral soybeans or full linen, should be excluded or reduced from the ration. Not advisable, if not in modest quantities especially in summer, are rich of oils byproducts such as rice husk, wheat bran, distillers, the corn germ extraction and soya and sunflower expellers also for

the negative effects that they have on fibers rumen fermentation and on the milk fat. The metabolic reorganization of the bovine prefers, for liver glucose synthesis, the propionic acid normally deriving from ruminal fermentation of starch and the glucogenetic aminoacids, to the point of looking for them in the muscle tissue. It is therefore good practice in summer to increase protein concentration of the ration using protein sources with low rumen degradability as corn gluten meal and, in critical cases, make use of rumen-protected methionine and lysine. During the summer, blood levels of hormones such as GH and IGF-1 reduces and this can also have negative effects not only on production but also on fertility, in particular because the IGF-1 is a “powerful” follicular growth factor. The production of IGF-1 is stimulated by aminoacids blood concentration. Greater availability in the liver of saturated fatty acids and aminoacids helps the hepatic synthesis of cholesterol, its export from the liver through the lipoproteins and therefore a higher cholesterol supply to the ovarian follicles for the synthesis of estrogen and

progesterone. In particular the latter hormone is declining in the summer. The summer lack of progesterone and high body temperature of the cow is the most obvious explanation for that part of summer infertility resulting from embryonic death. Sugars are also recommended, of which the rations for dairy cows are “chronically” lacking not so much to directly supply glucose, difficult thing in a ruminant, but for the action that they have on the attractiveness of the ration and as a growth factor of the rumen biomass. During summer time, sugars are preferred to starches, which concentration generally decreases in the summer, to avoid an aggravation of the already para-physiological

Increase protein in the ration

Use Aspergillus oryzae and Saccharomyces cerevisiae

Add sugars

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Environment & Management

by Alessandro Fantini

The importance of avoiding heat stress and overcrowding at the last stage of pregnancy

Dairy cows suffer overcrowding very much not so much for access to the manger as to the resting area. Furthermore there are departments such as the phase of dry and close-ups where overcrowding is the main risk factor for metabolic diseases as well as for low production and sub-fertility in the next lactation. In farms where the summer heat is not properly managed through cooling systems and adequate food, we can find both a decrease in milk production and a marked fertility reduction.In these farms there will again be pregnancies in late autumn and winter and then a concentration of calvings

in high summer, the well known worst period for calving of dairy cows. Having the calvings concentrated in summer and early fall means that many cows will spend the dry phase, or rather the last eight weeks of pregnancy, in hot overcrowded environments with a rather long light hours duration.These three conditions cause a subsequent lactation with not very high production and a low fertility. In fact the cows per capita production during fall, to equal days of lactation, will be lower than during spring in countries in the north of the equator. What solutions can be adopted to prevent this serious economic

loss? The first and most important it is to avoid summer infertility using electronic devices for the detection of heats, diets aimed at this and correctly cooling the lactating dairy cows. In any case it is important to care also about the dry cows with attention in trying to avoid overcrowding especially in the close-up while maintaining unchanged the duration of this phase. Where possible it can be of great interest to give access to an external paddock with shaded areas to dry and in preparation for calving cows. Also in this phase, should be predisposed fans and showers for cows cooling should be predisposed.

ruminal acidosis during summer. Very interesting is the use during summer, also on lactating cows, of propylene glycol which, as known, significantly increases the propionic acid intake without affecting the bovine rumen pH. Of great interest both for cows in late pregnancy than for those in lactation, is the increase of inputs of molecules that participate in the antioxidant system such as vitamin A, vitamin E, copper, zinc, manganese and selenium. In summer there is an objective and multifactorial difficulty of the immune system, especially of the cell mediated one. A testimony of this is the increase of somatic cells. It is therefore advisable in summer to

verify the actual intake of vitamin A and E and the possible adoption of chelated copper, zinc, manganese and selenium to really overcome the limits of intestinal absorption of inorganic molecules. This is valid for both dry and lactating cows. Finally, very useful are probiotics that belong to the kingdom of fungi such as Aspergillus oryzae and Saccharomyces cerevisiae.Particularly interesting is the fermen-tation medium of the Aspergillus as rich in enzymes useful for the hydro-lysis of food in the rumen. The use of these probiotics supports and facili-tates rumen fermentation, and then the production of microbial biomass and volatile fatty acids.

Proper management of the environment and nutrition during the summer can give a significant contribution to prevent the reduction in milk production and its main constituents such as fat and proteins, the summer infertility and the immunosuppression during both the peripartum and in full lactation. It will also give a secure contribution to the prevention of the “Syndrome of the low milk production in the fall” that causes an economic damage to the farms definitely higher than the one brought by the heat in the summer months.

Conclusions

Avoid overcrowding in the dry period and close-up

Improve the detection of heats to reduce the number of calvings in the end of summer

Fibrase, useful the association of BST Yeasts and BST Aspergillus strains

A research conducted by the Univer-sity of Bologna has investigated the effects of administering 20 grams per cow per day, under heat stress conditions, of Fibrase formulation (containing Saccharomyces cere-visiae, Kluyveromyces marxianus var. lactis, Aspergillus Oryzae and Aspergillus Niger). The study was carried on a dairy

farm in Lombardia (350 lactating cows milked through 8 milking robots), daily production data was recorded automatically by robots, milk fat and protein concentration measured weekly. Faeces were analysed to estimate influence of Fibrase on digestibility of fibre and the fibrous fraction.Fibrase has shown to be positively

effective on feed consumption (+ 0,467 kg per cow / per day in respect of control group), average milk production (difference of + 1,88 kg per cow /per day in respect of Control group), digestibility of ration and particularly in decrease of fibrous fractions (- 7% fibre, - 7% ADF, - 21% ADL Lignin less in respect of Control group faecis analysis).

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