Selective animal breeding already has almost 300 years of history. A lot has been achieved since. Obvious results have been achieved in the field of dog breeding. Selective breeding has produced very tall dogs like the Irish Wolfhound (>71 cm), very heavy dogs, like the Boerboel (50-80 kg), very small dogs like the Chihuahua (20 cm), very fast dogs like the Greyhound (17.5 m/sec), and very many more breeds with different looks and purposes. From 1960 onwards selective breeding in farm animals became very successful. E.g. in pigs between 1960 and 2010 the number of piglets weaned per sow per year increased from 14 to more than 30. The amount of lean meat per ton of feed increased in that period from 85 to 170 kgs due to a higher lean percentage and a better feed conversion. In layers in that period the amount of eggs per hen housed increased from 230 to 370 and the eggs produced per ton of feed from 5000 to 9000.
1.12.1 Results obtained in cattle breeding
The size of the genetic improvement from generation to generation depends on the technique used to select animals for breeding. Introduction of new selection techniques made it possible to select the best animals for breeding more accurately and efficiently. Especially the introduction of reproduction techniques like artificial insemination (AI), that made it possible to have (very) large numbers of offspring per sire, made it possible to select only the very best males for breeding, without decreasing the population in size. In females techniques like embryo transplantation (ET) or ovum pickup have made it possible to produce much larger number of offspring of excellent females than with normal reproduction techniques in this species where normally only one or few offspring per year were feasible. The wide use of these reproduction techniques resulted e.g. in a steady increase of the milk production per cow.
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In figure above on the left, you see the increase in milk production in the Netherlands between 1945 and 2022. The increase until 1970 is much less steep than that from 1990 onwards. Reasons for this are many, but important ones are, in addition to the application of reproduction techniques, the introduction of more accurate techniques for estimating breeding values, introduction of automatic milking and the free stall instead of the tied stall, and better quality of the diet. In the graph on the right is the phenotypic trend compared to the genetic trend in the period 1995 – 2022. You see that the increase in phenotypic (= realised) milk production in that period is very similar to the estimated increase in genetic potential for milk production: in both cases approximately 2000 kg. This indicates that systematic improvements in the environment such as automatic milking, loose housing, and diet quality has similar effects on all cows.
1.12.2 Results obtained in pig breeding
One of the terminal sire lines of Topigs Norsvin is the TN Tempo line. In the past 5 years the relative weight of daily gain and feed conversion was 45 per cent. It resulted in an increase in daily gain of 120 grams and from 30-120 kgs of weight 24 kg of feed was saved.
The Topigs Norsvin finishers are produced by the TN70 crossbred sows. The figures below illustrate the steady increase in litter size, survival rate and number of teats. And the longevity and fertility of sows improved as well.
1.12.3 Results obtained in layer’s egg production
In egg production the total egg production per hen housed is an important economic trait. In recent years the selection was aimed at a constant production (one egg per day) and a high persistence leading to a longer productive period of hens raised. The figure below, supplied by Hendrix Genetics, illustrates the selection results obtained between 2008 and 2023: a higher egg production per hen housed through a better and more persistent production and the extended laying period.
1.12.4 Results obtained in broiler production
Source: Zuidhof et al 2014. Editor's choice: Growth, efficiency, and yield of commercial broilers from 1957, 1978, and 2005 - PMC (nih.gov)
The effect of commercial selection on the growth, efficiency, and yield of broilers was studied using 2 University of Alberta Meat Control strains selected since 1957 and 1978, and a commercial Ross 308 strain (2005). Mixed-sex chicks (n = 180 per strain) were placed into 4 replicate pens per strain, and grown on a current nutritional program to 56 days of age. Weekly front and side photographs of 8 birds per strain were collected and the results are shown in this figure:
From 1957 to 2005, broiler growth increased by over 400%, with a concurrent 50% reduction in feed conversion ratio, corresponding to a compound annual rate of increase in 42 d live BW of 3.30%. Forty-two-day FCR decreased by 2.55% each year over the same 48-yr period. Pectoralis major (chest muscle) growth potential increased, whereas abdominal fat decreased due to genetic selection pressure over the same time period. From 1957 to 2005, pectoralis major yield at 42 d of age was 79% higher in males and 85% higher in females. Over almost 50 years of commercial quantitative genetic selection pressure, the intended beneficial changes have been indeed achieved.
1.12.5 Breeding results in racehorses (trotters)
In several countries horse racing is a popular sport with as an important aspect for the public: gambling on the winner with monetary prices. It is comprehensible that for speed the heritability is not high: for the sprint and middle-distance 0.12 and for the long distance 0.07. The effects of trainers and jockeys and the circumstances on the racetrack have a major effect on the performance of the horse. Despite a low heritability and a long generation interval, a steady rise in estimated breeding value is observed especially for the sprint and middle-distance as can be seen in the figure below.
