66 THE CATTLE OF GREAT BRITAIN. 



under cover." Treating of a breeding farm, and animals of all 

 ages from a year upwards, we consider that the saving of food 

 for a given result will certainly average 6d. a head per week, 

 which for eight months comes to 16s. Therefore the saving by 

 covered yards in manure, litter, and food comes to 



£ s. d. 



Increased value of manure 18 



Saving of straw 1 



Saving of food 16 



Total per head £2 14 



Enough has been advanced to prove that the use of properly- 

 constructed covered yards is one of the greatest and most 

 important of modern economies, which should engage the 

 careful attention of all who are interested in agriculture. 



4. Details of Construction. — In a short sketch like this we are 

 unable to do more than very briefly touch upon certain general 

 considerations. We have a considerable choice as to method of 

 construction and materials. Galvanised iron has been largely 

 used, and as the price of iron is so moderate it is quite possible 

 that as regards first cost, such are not dearer than wooden 

 roofs and open slating ; but there are three objections which 

 militate against iron. Ventilation is less perfect ; the galvanising 

 coating is liable to injury from gaseous emanations, both from 

 the animals and the manure when being removed. Painting 

 occasionally will diminish this risk, but adds to expense, and, 

 thirdly, iron roofs are hot in summer and cold in winter. 

 Ordinary framed roofs, with principals, purlins, and rafters, may 

 be used for small spans, and are necessary when a heavy covering 

 like pantiles or Bridgewater tiles are used, but there is a limit 

 soon reached as to the spans of such roofs. For large spans up 

 to from 50ft. to 60ft., a series of ribs combining the bow string 

 girders with rafters at a pitch suitable for slates placed 9ft. 

 apart, supporting purlins carrying two rafters 3ft. apart, on 

 which strong laths, IJin. by IJin., are nailed at intervals of 

 about Sin. to carry the slates, forms a roof which, very light in 

 appearance, possesses great strength, owing to the distribution 

 of strain over every part which may be judged of from 

 the fact that for such a span the maximum scantlings of 



