Frequency polygons showing the seasonal distribution of birth dates in Poland ond peak in the autumn months September and October. In the North Central Zone (II.) this tendency to bimodality becomes much more pronounced and there is a distinct second peak produced by the farrowing in the autumn. As we proceed to the South Central (III.) and Southern (IV.) Zones the curve becomes more and more flat topped, indicating less and less tendency to segregate the breeding period to any one particular season of the year. The spring mode, however, is not entirely lost, even in the southernmost zone. (b) The effect of this tendency to a secondary autumn farrowing season is to advance the average birth date of swine as we proceed from north to south. In the case of the Poland China records this difference in mean birth dates between the north and south amounts, in the extreme, to about a month and a half, and in the Duroc Jerseys to about a month. Another result of the same tendency is, of course, to make the variations in birth dates, as indicated by the standard deviation, larger as we proceed southward. (c) While there are minor differences in the distribution for the two breeds, it is clear that the breeding follows substantially the same rule in both. The maximum difference is in Zone IV., where there is a difference of 123.99 days between the means, an amount almost exactly 3 times the probable error, and of doubtful significance. (d) To get a rough but sufficiently accurate general index of hog breeding conditions we may combine the figures for the two breeds. This process gives the distributions exhibited in Table VI. (e) The essentially bimodal character of the swine breeding curve appears clearly from Table VI. There is a distinct autumn mode but it is only from 20 to 25 per cent. as high as the spring mode. Broadly speaking about three fourths of all the pigs are born in the first half of the year. According to the official statistics of the Department of Agriculture nearly one half of the country's total hog population is included in our Zone II. Probably this zone contributes two thirds to three quarters of the commercially slaughtered hogs. In Zone II. the following relations hold: 47.3 per cent. of all pigs are born between January 1 and April 1. Or, in other words, in the chief swine growing region of the country nearly one half of the pigs are born in the first quarter of the year, and over three quarters of the whole number of pigs are born in the first five months of the year. This assumes of course that we may take the samples of the two breeds here dealt with as indicative of the whole population, which I think we can to a sufficient degree of accuracy. 5. It is of interest now to consider the marketing or slaughter curve for hogs. The Bureau of Animal Industry of the Department of Agriculture maintains some nine hundred stations throughout the country for the inspection of all meat animals received for slaughter. These stations do not cover all the slaughter in the country, but only that of the larger centers slaughtering for interstate shipments; however, they represent in the case of hogs 58.9 per cent. and in the case of cattle 56.4 per cent. of the total slaughter of the country, as determined from the 1910 census. The following table presents the average percentage that each month's inspection bears to the total for the calendar year, computed from the reported inspections for the six years ending December 31, 1916. The percentages of Table VII. are shown graphically in Fig. 2, on which is also given for comparison the birth curve in terms of percentage. From the table and the diagram it is evident that the slaughter follows a very different curve than the births. The most essential point of difference is that the slaughter is much more evenly distributed over the year than the births. The 2 Cf. Finch, V. C., and Baker, O. E., "Geography of the World's Agriculture," U. S. Dept. Agr., 1917, pp. 130-132. FIG. 2. Diagram showing the monthly slaughter under inspection (solid line) of hogs, expressed as percentage of total slaughter for the year, in comparison with the monthly birth rate (dash line), again expressed as percentage of the year's total. TABLE VII INSPECTION FOR SLAUGHTER Per Cent. that each Month bears to Total for the Calendar Year former curve shows no such violent fluctuations as the latter. During the hot months of the year, July, August and September, the shipments are only about one half those of the winter months, because properly conditioned hogs will not stand shipment and losses are heavy. As the cooler weather comes on, the heavier movement begins and reaches its maximum in December and January, with a decline in each of the succeeding months until May and June, when there is another increase. The two high points of the year in December and June reflect the marketing of the two crops of pigs, spring and autumn, that are produced each year, but in a much reduced degree. 6. What the above facts mean is that there is much more variability on the part of the farmer in the finishing of his pigs than in the breeding of them. To a very considerable extent this removes the potential danger to the nation's food supply which inheres in having 41 per cent. of the nutrient fat supply produced from a source of which 75 per cent. comes into existence in less than one half of the year. The data in this paper show that for all practical purposes the danger point which wants watching is the absolute number of pigs born, not their distribution in different seasons of the year. |